Bite mark forensics bite the dust in Texas

Way back when, monsters like Ted Bundy were taken off the streets in part because of a relatively new scientific field called bite-mark forensics. The idea was that the arrangement of teeth in a suspect’s mouth would leave a signature bite mark. If that bite mark could be traced back to a suspect, then this was proof that the bite had to have come from his or her mouth.

The only downside to that concept was that it never had a single shred of scientific proof that it worked. Nothing at all.

The problem with bite mark analysis is that, while it is true that a mouth full of teeth will leave a distinct pattern on something flat and immobile, most things in this world are not quite so perfectly constructed for bite mark analysis. in the particularly ghoulish case of tooth marks in flesh, the flesh tends to bend and warp and flesh does. This renders what little reliability bite-mark forensics has moot.

So, this is another one of those cases where forensic science is getting gut-punched while case after case is overturned on the basis of evidence once presented to us as infallible.

Bite mark forensics is the study of how bite marks can be used to identify the dental “signature” of an individual. Such evidence has been used to convict Ted Bundy, among others.

Source: Texas bans the use of bite mark forensics in court cases – DragonFlyEye.Net

Anthropology Archeology Forensics Genetics Science

DNA in Doubt: our increasingly-complicated relationship with the stuff of life

It used to be so uncomplicated. DNA is the stuff that makes you who you are. It’s what makes you look the way you do, makes you susceptible or resistant to certain types of illnesses, even sets your biological clock. DNA is the stuff of life.

Except when it’s not. As science probes the depths of the genomes of all forms of life on Earth, we are confronted with an increasingly-convoluted relationship between DNA and it’s expression – nature and nurture, in other words – that in turn makes our previous use of DNA increasingly dubious.

Sammy Malone: DNA forensic expert
Y’know, Sammy Malone: crime fighter.

It isn’t all bad news: our more sophisticated understanding of genetic information means we’re getting close to finding cures for disease, genetically-tailored health care and amazing discoveries in the worlds of biology and anthropology. But our colloquial understanding the nature of DNA has not caught up to the scientific understanding. The result of this gap can often be abusive at best and flat out destructive at it’s worst.

Nowhere is that fact more certain than in the world of forensics. As DFE discussed last year, local law enforcement has seen the same forceful push-back on DNA evidence presented in criminal cases that has swept the nation in the last few years. The assumption most of the public has in the infallibility of DNA to finger guilty parties is entirely wrong. And whether intentionally or not, many cases have been tried and many people convicted on evidence that is nowhere near near as declarative as prosecutors would have you believe.

A new grant to Syracuse University is aimed at finding a solution to a fundamental problem in forensic DNA evidence-gathering: mixed DNA samples. Regardless of what type of tissue law enforcement is sampling from – blood, semen, hair, skin – it’s still just a pile goo at a crime scene. That pile of goo is a bit of a hothouse flower: organic chemicals don’t last long outside the body. And biological evidence can easily get mixed up with other that of individuals not even involved in the crime. Taken together, you can see that this is a bit of a dumpster dive.

So clearly, the biggest challenge in DNA forensics is getting a clean, uncontaminated and complete sample of DNA. How challenging? Basically, the odds of meeting all three criteria are just a few degrees north of ever french kissing a unicorn. Pretty low.

The SU plan is to light up cells with dyes and black light in a way that lets them tell whether the two cells contain the same DNA. The next step would be to extract them by DNA signatures: all of Specimen X, followed by Specimen Y and so on. That’s where SU’s brain power is supposed to hopefully kick in.

And even as the scientific community grapples with the problem of commingling DNA and incomplete samples, a novel and highly-dubious use of DNA evidence is being tested in law enforcement, winkingly called “Familial DNA.” This concept means that, even if you’ve never been DNA tested for any reason, your DNA may get linked to a crime, simply because there is DNA in a database from a cousin or other relative.

What? That’s right. If a DNA sample taken at a crime scene is similar enough to a relation of yours, police may use this fact to posit that the DNA must be yours. In a Six Degrees of Separation type of scheme, you are implicated to be involved in the crime simply because you have similar DNA to what was found on scene.

This deeply-troubling practice runs directly afoul of the Birthday Paradox, a statistical quirk that radically and unexpectedly reduces the odds that a match will be found in a group, rather than individually. For a much more elegant explaination than I might summon forth, read Southern Fried Science. This statistical fact makes DNA databases generally misleading in the first place, but once you expand the search to include people who aren’t even in the database, the potential results are genuinely disturbing.

In the world of anthropology (the science, not the store), our deepening understanding of mitochondrial DNA is completely redefining our understanding of human migration. Perhaps not for the better, depending on your favourite theory.

At issue is the long-held belief that those who would become Native Americans traveled across the Land Bridge and very quickly populated the whole of the Pacific shore. This fairly linear theory of American anthropology has brought multiple theories and timelines into clash for decades. Are the Clovis points really the most ancient relics? No. But are the Clovis people still the oldest people in the Americas? Well, maybe…

What the newest mitochondrial DNA evidence, taken from the bones of a mother and child discovered near the Bering Sea, suggest that perhaps part of the problem with identifying the path of Native Americans is that there simply isn’t just one path.

Instead, the mitochondrial evidence points to a highly-diverse group of Asian immigrants coming across the famed land bridge. Rather than a single set of tribes or related individuals crossing the great divide, it may have been hundreds. This new evidence suggests that the reason archeological evidence of human inhabitation seems so scattered is because human habitation was in fact very scattered.

If there is a lesson in the week’s DNA news stories, it is that science is a double edged sword for those that would hold onto it’s truths too tightly. However reliable a scientific fact has seemed in the past, there is always new research that casts doubt upon it.


Charles Tan: did the prosecution just phone this one in?

On September 29th, the closing arguments in the Charles Tan murder trial took the whole process from strange to bizarre. After the Tan defense team decided – for the first time in the trial – to directly finger Charles’ mom as the culprit, the prosecution just seems to have gone off the rails. Rare as it is to see gunplay in a Rochester courthouse, it’s even less likely to see a prosecutor waving one around in people’s faces.

Honestly: it really seems from outside the courtroom that the prosecutor just didn’t see this sudden defensive play coming.

If he didn’t see it coming, certainly most of the rest of us did not. In fact, looking back, it’s sort of strange just how quickly the narrative of Charlie Tan, Amazing Young Victim, developed after the initial reports. Almost as soon as we heard Charles Tan’s name, the narrative already seemed set in stone. He is a victim of domestic violence – no one disputes that even now – and an otherwise upstanding citizen and student. Charlie, we heard from almost every quarter, was nowhere near this evil.

And I think most of us, lulled into this bedtime story of Charlie the Innocent, expected the trial to be quick and easy. Whether you thought he was going in the tank or not, everyone seems to have been assuming that this was going to be straight forward. It turns out to be nothing of the sort.

Did the prosecution get lulled as well? It feels like they were. Not solely because of the drama of yesterday’s closing statements.

More so, it seems like a high-profile case like this wouldn’t even make it into court without much more evidence. We have all been treated to the gory details of the crime scene – a body sitting dead for at least a few days, a dog having eaten the carcass. But gory details don’t prove who did it, and on this level, the law seems to have stopped well short of doing due diligence.

Because the question of whether Jean or Charles Tan committed the crime really feels like it should have been the first thing they checked out. Yes, there was a confession. No, neither Charles nor Jean seem to have been willing to cooperate with any other leads. But if this had been some brother on Child St, you can bet the cops would have grilled him within an inch of his life if they’d thought he wasn’t being straight.

Are rich people from Pittsford simply too beyond the pale to grill? Did everybody just assume Charles was telling the truth? If he was, why was there a days-old body when cops arrived? How is a days-old dead body not cause for some intense examination, regardless of what anyone says on the scene?

Maybe no one is all that interested in justice for the victim in this case. I can hardly blame anyone for feeling that way. But a crime was committed. Even if I can appreciate the well-founded contempt for Jim Tan and can hope for the best for a victim of domestic violence, our society, not Jim Tan, deserves a conviction in this case. And we don’t even know whom to convict.

More on Charles Tan


Charles Tan: estimating time of death isn’t as simple as it sounds

On Monday evening, February 9th, police were called to the Pittsford home of the CEO of Dynamax Imaging, Liang Tan. His son Charles Tan later confessed to killing his father with several shotgun shots to the chest that evening. But the D&C is reporting that new evidence suggest that perhaps Tan’s body had laid where it was for more than a day before the police were contacted.

How can there be this much ambiguity about when Tan was shot? To most people, this would seem like the kind of thing forensic science would have down, well, cold by now. Shouldn’t such a basic fact of forensics be a quickly-determined, reliable thing?

The truth is: determining time of death is not a straightforward, formulaic process. It is a bit of an art form, requiring years of experience and careful attention to the most minute of details. And many of the clues to determining when a victim was killed are only available for a limited amount of time.

Time of Death on the Scene:

The first line of defense in a murder case is always the police on the scene. However long the body may have laid in place, the police that first arrive at the scene are the officials with the most recent contact and therefore least likely to miss evidence. Only a medical examiner (ME) or coroner can officially declare a victim dead.

Every bit of evidence is important, and nothing can be disregarded. Some of the evidence gathering would surprise some people in it’s crude methodology. One of the most basic forms of forensic evidence is to see if the victim is wearing a watch. If so, did it stop? The time on the watch offers some clues as to the time of death.

Other means of determining the time of death on scene include investigating the body for clues. The temperature of the body, it’s discoloration and the set-in of rigor mortis are all clues to the time of death. As a rule of thumb, bodies typically cool at a rate of about 1.5 degrees centigrade per hour. Rigor mortis sets in after about 12 hours. Other factors, like the amount of blood that has coagulated on the floor can also be used as clues. Here, thanks to a forensics blog, is a helpful guide to some critically-timed physiological events:

1-2 hours: ………Early signs of lividity.
2-5 hours: ………Clear signs of lividity throughout body.
5-7 hours: ………Rigor mortis begins in face.
8-12 hours: …….Rigor mortis established throughout the body, extending to arms and legs
12 hours: ……….Body has cooled to about 25°C internally.
20-24 hours: …..Body has cooled to surrounding temperature.
24 hours: ……….Rigor mortis begins to disappear from the body in  roughly the same order as it appeared.
36 hours: ……….Rigor mortis has completely disappeared.
48 hours: ……….Body discolouration shows that decomposition is beginning.

“Lividity” refers to the pooling of blood inside the body as it remains inactive and the heart stopped. As you can see, lividity – or liver mortis – is not an effective means of determining time of death past a very limited window.

In the lab, they can also test for the presence of parasitic insect larvae. After a body is completely dead, insects tend to use the body as a place to lay their eggs. An entire branch of forensic sciences is concerned solely with “forensic entomology,” or the study of the insects whose trail can be used as evidence. There are many more tests they can run in the lab, but by then, all the most immediate signs of death have long since vanished. This is why it is critical to get the evidence right on-scene.

.. But the Charles Tan Case is More Complicated:

When it comes to inspecting the body, things are dicey on-scene. That’s because the condition of the body can’t be separated from it’s circumstances. The ambient temperature of the scene, the presence of scavengers or any number of other factors all play a part in contributing to the body’s state. This winter has been one of the coldest in recent memory, and that factors into how all of these observations are interpreted. Also, because Charles Tan claimed to have killed his father that evening, it is possible that critical evidence was missed based on an assumption.

Bodies lose heat as they sit, of course. But while the rule of thumb is 1.5 degree centigrade per hour, that rule means little in especially frosty days like those we’re experiencing now. Reports so far don’t indicate where the body was found. But the shotgun was found in the garage. If he was shot in the garage and left there for a while, his body would have been a good deal colder than expected.

Even the classic sign of death – rigor mortis – is not a permanent condition. As you can see from the chart above, rigor mortis sets in within about twelve four hours after a victim has died. But it is completely gone within 36 hours. In the Tan case, that may have been the factor that threw off the initial time of death estimation – if it was assumed that Tan was shot recently then the investigators would have expected no signs of rigor mortis. And if indeed the murder took place a day before police were called, there would be no sign of rigor mortis by the time officials got to the scene.

What about insect larvae? There were not likely to be many insects in the middle of the winter. Ergo there’s not going to be a lot to go on in that sense. As I write this, no new details have been released on this case. You can expect the Medical Examiner’s Office is going over every single detail with a fine-toothed comb and inspecting the body for every last detail.

It remains to be seen exactly where and when Liang Tan lost his life and most details will never be made public. This will almost certainly include most of the forensic evidence. Whatever the truth is, it will largely be the corroboration of forensic evidence with witness statements and those of Charles Tan that will be the deciding factor.

Crime Forensics Science

Stewart, Ward Jr and the forensic toxicology of weed.

On the evening of August 9th, 2014, an altercation on Canandaigua Motor Speedway’s muddy track resulted in the death of a 20 year old racer. The heavy metal I grew up watching; the mud, blood and dirt of of a small track speedway; the testosterone that drives so much of it’s checkered past and dominates it’s present. All of it met that night, to deadly effect. Last week, the Livingston County prosecutors, in acquitting Tony Stewart of all charges, charged that Kevin Ward, Jr may have had enough marijuana in his system to have impaired his judgement.

Common knowledge has it that marijuana stays in your system up to two months at testable levels. How then could a forensic test determine that Ward, Jr was high at the moment of his untimely end? Or is that just more prosecutorial flourish than fact?

The biology of pot metabolism.

To begin with, we need to understand a bit of the basics of how cannabis is metabolized – or broken down – by the body. There are essentially two major phases of this process which create two distinct metabolites: hydroxy-THC and carboxy-THC.

The first phase of metabolization takes the raw THC that the subject smoked, ate or otherwise consumed and creates hydroxy-THC (THC-OH). Basically, the body takes the THC molecule and sticks a hydroxyl group on to one side – a pair of oxygen and hydrogen (OH). This is a relatively swift process, taking an estimated 4-6 hours to complete. hydroxy-THC is not a psychoactive drug any longer, however, some studies have suggested that the “munchies” happen a few hours after smoking pot specifically because of the break down of this particular metabolite into…

Carboxy-THC (THC-COOH) is the next phase of metabolism. At this point, the body has added a carbon and another oxygen to the original pair, creating what is known as a “Carboxyl Group,” or COOH. Carboxy-THC is an inactive chemical, pharmacologically speaking, and more or less the end of the road of anything that looks like THC. But this is one of the chemicals that drug tests that you might take for pre-employment screening test for. This is the one that lasts two, three or more months in the body.

What does this mean for testing?

Because there are two distinct metabolites – and because one has a lifecycle of only 6 or so hours – it is possible to at least determine within a range of hours how recently a person smoked pot. And based on a comparison of the amount of hydroxy- and carboxy-THC it is even possible to determine just how high someone might have been at the time of death.

But there are caveats, and they’re important ones.

First, as with all toxicology reporting, a person’s height, weight, body mass index and general health all play in as factors in determining how quickly the body can break down hydroxy-THC. Also, because hydroxy- becomes carboxy-THC and a heavy smoker can be assumed to have high levels of carboxy-THC, frequent pot smokers are going to take longer than infrequent smokers to break down the hydroxy-THC.

All of these factors make determining exact amounts or times more or less impossible. For this reason, similar toxicology reporting has been either thrown out of court or else disregarded by juries. There are enough questions surrounding this type of test that prosecutors have so far had a difficult time convicting people based on this type of evidence.

In this case, however, forensic investigators have one major point in their favour, in that Kevin Ward, Jr is unfortunately dead. Convicting a living person of driving while intoxicated is hard, at least in part because somewhere between arrest and blood testing, hours may have passed. It’s just too easy to explain away a window of 4 to 6 hours.

But when a person dies, the metabolic clock stops. We can safely say that a person died at a specific time, and working back from there, we can compare the hydroxy- and carboxy-THC levels in the body and say that Kevin Ward, Jr was or was not high within a reasonable doubt. Thus based on the evidence I’ve been able to gather, it is at least a possibility that the prosecution’s contention in this case is based on solid evidence.

I attempted to contact quite a few forensics experts on this subject, but sadly, could not get a response in time for this article to be published.

Forensics Science

Resting on shaky ground: did DA Doorley mislead a jury on faulty DNA evidence?

Some truths are axiomatic. They’re ideas we hold as being so solidly true, we never bother to examine them too deeply.

The concept of “DNA evidence” as the fool-proof smoking gun is one of these axioms. We understand that your personal DNA encoding is responsible for determining your sex, hair color, eye color and even your risk of having a heart attack. We know that, when a person interacts with a crime scene, there’s a distinct possibility that they may leave behind substances from which DNA can be sampled and a match found. There’s even new technology aimed at potentially reconstructing your face from DNA, to help police search you out.

But is DNA evidence presented in court really so iron-clad? What exactly constitutes a “match” by forensic standards, and how close can that match be to the true criminal? These questions were put to the test just recently in the appeals trial for Howard Wright, charged with the 1995 rape and murder of Patricia Daggett. The conviction was ultimately upheld on a 3-2 vote, but the two judges that dissented point out that the DNA evidence was nowhere near as conclusive as they contend then Assistant District Attorney Sandra Doorley made it seem. Indeed, based on court documents, it very clearly was not. The dissent reads in part:

As the majority notes, the People “presented evidence that . . . defendant’s DNA could not be excluded from various pieces of evidence recovered [from the victim’s vehicle].” At trial, the People’s forensic expert, who analyzed defendant’s DNA sample, described the two types of DNA testing used in this case—mitochondrial DNA analysis and YSTR DNA analysis…

The People’s forensic expert acknowledged the two above-mentioned types of DNA analysis at trial, but she did not speak at length about a third type of DNA analysis—autosomal..

How could an analysis of DNA evidence not point solidly to a single individual? The dissent notes that the sample could not have ruled out the victim’s husband, nor could it rule out the second alleged accomplice in the crime, Christopher Gifford. And what are these three types of DNA testing?

The DNA of DNA forensic testing

To unravel this mystery, we first need to understand that not all DNA in your body is the same. There are two types: nucleic DNA and mitochondrial DNA.

Nucleic DNA is a combination of information from your genetic parents, which is passed to you, and is responsible for the you-building that we all understand. Mitochondrial DNA is passed more or less unchanged from your genetic mother to you. Mitochondrial DNA does not contain enough information to be used to pinpoint a specific individual, but can be used to broadly exclude individuals who simply do not match.

That leaves us with nucleic DNA. But here again, there are two different types of testing, YSTR and autosomal. YSTR tests are performed on the Y chromosome and therefore only possible in male individuals. But since the Y chromosome is passed intact from father to son, all individuals of a specific paternal line – which could potentially be quite vast – will have similar or exactly the same YSTR results.

Autosomal DNA testing is the closest thing in the forensic arsenal to the “smoking gun.” In autosomal testing, 22 out of the 23 pairs of chromosomes that make you what you are can be tested. The 23rd pair is, of course, the sex pair for which YSTR is used. Here is the evidence which sometimes boasts a 1-in-a-billion accuracy.

Then what of Mr. Wright’s sentence?

Regardless of which method of testing is used, the results boil down to a statistical analysis and professional judgement of the facts of the case. And none of these types of evidence is easy to get in the first place. DNA like all living material is delicate and easily destroyed at the scene of the crime, by investigators or even by the lab.

Mitochondrial and YSTR testing can certainly be used to exclude a suspect from consideration, assuming that their DNA signatures differ significantly enough. But they don’t do much to identify a specific suspect, especially as in this case, where multiple persons involved in the crime all fit the same basic profile. Only autosomal DNA testing can positively identify a single individual, but that requires a working, undamaged sample of all 22 required pairs.

The dissent for Mr. Wright’s appeal says that the People’s forensic expert never spoke “at length” about autosomal DNA evidence. Was that because that evidence was not conclusive, or not possible to obtain? Nobody says.

Other evidence presented in the case, as recounted by the appeal ruling, is deeply suspicious but circumstantial. Wright was seen in Daggett’s car with her prior to the murder; the prosecution proved that Daggett was raped in the car; eye witnesses saw Wright in Daggett’s car the next day. None of these facts would have been usable for a conviction on their own, without DNA evidence. But the DNA analysis was itself dubious and inconclusive: it implicates three potential suspects, one of whom was never on trial.

The real problem here is not whether the DNA matched one individual suspect. The real problem seems to be that the fate of our justice system was in this case settled by a 3-to-2 decision in which the majority seems to whistle past a very large graveyard. The majority waves a fairly vague hand at the DNA evidence and concludes, based on circumstantial evidence, that a “reasonable person” might have found Mr. Wright guilty. In the absence of the DNA, is that really true?

If sympathy for the convicted is hard to come by, it is worth considering the implications of a 3-to-2 decision in the opposite direction. Had the flimsiness of the DNA evidence been the thing that overturned the conviction of Howard Wright, how many more men in how many more jails might have been set free, possibly erroneously, on the basis of dubious forensic evidence gathering?