EvidenceProf Blog

Editor: Colin Miller
Univ. of South Carolina School of Law

Saturday, January 16, 2016

Is Jerry Buting's Claim About Sweat DNA Correct?

One of the trial attorneys for "Making a Murder" subject Steven Avery

called out former District Attorney Ken Kratz for “continuing his public misinformation campaign.” 

“He is making statements he should know are untrue, like claims about Steven Avery’s ‘sweat DNA’ being found on the hood latch of the Rav4,” says [Jerry] Buting. “There is no such thing as ‘sweat DNA.’ DNA is found in all nucleated cells, but there has never been a test to determine that a sample of DNA came specifically from perspiration.” 

He adds: “What Attorney Kratz also has not mentioned is that there are many studies that show ‘touch DNA’ can be innocently transferred from one object to another, or one person to another, without any connection to a crime. 

Is he right?

Yes. It is well established that "sweat contains no DNA." Brief of Appellee, Ashcraft v. State of Indiana, 2012 WL 4937683 (Ind.App. 2012). That said, "people often slough off skin cells containing DNA when they sweat; thus, DNA is often present on articles of clothing, including hats." State v. Norman, 2003 WL 22999499 (Ohip App. 2003).

As Buting noted, DNA is found in all nucleated cells:

DNA is the chemical which encodes all genetic information. DNA is located in the nucleus of all nucleated cells in the human body, remains constant throughout a person's life, and is identical in each cell-i.e., the DNA extracted from a man's blood cells is identical to the DNA extracted from his sperm cells. Each person's DNA is unique, with the exception of that of identical twins....

DNA is composed of two strands made of chains of chemical bases called nucleotides. Each nucleotide is one of four chemicals which compose a four-letter organic alphabet. The strands are very long, containing billions of nucleotides which can be arranged in any order along the strand. The order of the nucleotides determines certain characteristics which will be expressed in an individual's physical or mental traits. Each sequence of nucleotides which encodes for a specific characteristic is a gene, and can be thought of as one word using the four-letter alphabet. The two strands are joined together and twisted into a shape referred to as a double helix, which can be envisioned schematically as a twisted ladder. The order of the nucleotides on the opposing strand is complementary in that certain nucleotides always pair with one another. It is possible to separate the two strands of DNA, and they will rejoin in the original manner because of the specific ways nucleotides pair with one another. State v. Pennington, 393 S.E.2d 847 (N.C. 1990).

As a result, as Buting claimed, there is no test to determine whether DNA came from skin cells in sweat or other nucleated cells. As Dr. Ann Hunt testified in State v. Ramsey, 2010 WL 9070062 (Mich.Cir.Ct. 2010):

Q. What other fluids or aspects of the body contain all that?

A. Any nucleated cells in the body would contain DNA. So, um, in our, in our forensic work we basically work with um, white blood cells will have a, a large amount of DNA. Um, skin cells again. We work with, as a known sample we ask for a swabbing from the inside cheek area because there's a very high level of um, nucleated cells inside the cheek. Um, semen samples. Ah, the apiifolia cells from the female, um, in a sexual assault case have a very high yield of DNA. And then the sperm cells also, um, contain DNA so we can do comparisons on those samples as well. We've gotten numerous samples from chewing gum, to lollipop sticks, to um, just anything that would contain what we would um, expect to find nucleated cells on.

Q. Sweat from sweat glands, is that?

A. The cells, the nucleated cells that are shed in um, sweat would contain the DNA.

Q. OK. Now ah, can DNA anywhere, I mean not just here, but anywhere in, in the nation, can DNA tell you as a lab person for instance when ah, a certain act occurred, or when a piece of clothing was worn, can it tell you that?

A. Um, there are serological tests um, for example, in sexual assault cases where we can um, have a time frame um, sperm cells will only last in an individual's body for so long. On clothing garments, um, until an item is washed, um the DNA is relatively stable in a dried state. Um, so I wouldn't be able to give a time frame on a dried item of clothing material.

Q. And I guess, that was a good answer to a bad question. In other words, what I'm looking or what I'm asking you is that, ah, you can tell from DNA analysis if somebody wore a particular piece of clothing. But can you tell when they wore it?

A. Um, we can include or exclude an individual as being a potential donor to DNA found on a clothing item. However, a, a time frame would not be possible.

The first part of this testimony establishes that you can't tell whether DNA can from skin cells in sweat as opposed to any other nucleated cells. Here's further testimony on the subject by Dr. Christopher Chillseyzn in State v. Gaudette, 2005 WL 6958954 (N.J.Super.L. 2005), indicating that it's impossible to distinguish DNA in sweat/skin from other DNA.

Q. And DNA from epithelial skin as opposed to say DNA from sweat, is it different or is it going to come out all the same if it's the same person? Jessica's epithelial DNA --

A. All cells in the body contain, well, except for sex cells, all cells will contain the same DNA from any tissue type from any person.

Q. So looking for Jessica's DNA on Jessica's shirt, would that tell you whether that came from saliva or sweat, could you differentiate?

A. No. Well, sweat itself wouldn't contain the DNA. Epithelial cells that the sweat washes off that has the DNA. But no, I wouldn't be able to tell. (emphases added).

The second part of Dr. Hunt's testimony establishes that you can't determine when the DNA was left behind, which is a question that a few readers have asked me.

Finally, what about Buting's reference to touch DNA? I will cover that when I write my post on the final episode of the Unsolved Podcast.



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Really interesting information; thanks. Every time I hear something from Kratz I want to punch him in the throat, and I'm less inclined to believe him, so it's good to know that at least some of the words he's spewing have no basis in fact.

Posted by: Beth | Jan 17, 2016 9:29:44 AM

Especially relevant since Dean Strang (the other defence attorney) said the forensic investigator admitted to not changing gloves between collecting the blood evidence inside the car and the so-called "sweat DNA" on the hood latch. Avery could be the second coming of Jack the Ripper and a lot of folks involved in this prosecution should still be looking for other lines of work.

Posted by: Amanda | Jan 17, 2016 4:44:30 PM

Much appreciated, Colin. As always, your analysis on these matters carries a lot of factual weight, and glad to hear this confirmed from an unrelated 3rd party. Any chance you could get this info to Nancy Grace, so she'll stop it already? :)

Posted by: Emily | Jan 18, 2016 10:33:23 AM

Whilst the DNA itself doesn’t tell you anything about where in the body it comes from, are there not other ways to place the DNA? E.g. whole skin cells and, say, cheek cells look different and can be told apart under a microscope; sweat contains salt; saliva contains enzymes – the references you mention are only talking about the DNA itself. (And why is the DA calling it ‘sweat DNA’ anyway – is there some other evidence/theory that’s leading him to say that? – If not, why not just say ‘DNA’?).

Posted by: Cupcake | Jan 18, 2016 10:42:50 AM

To make Steven Avery look like a sweaty, dirty monster? His opponents always emphasize how sweaty he is, as if that were an indicator of guilt.

Posted by: Anna | Jan 18, 2016 3:29:28 PM

Beth: You’re welcome.

Amanda: This gets into the whole “touch DNA” analysis.

Emily: I can send it along.

Cupcake: I don’t know why he’s calling it “sweat DNA.” I’ll have to look into that.

Posted by: Colin Miller | Jan 18, 2016 6:45:27 PM

Could a DNA sample be transferred from a used toothbrush? Curious.

Posted by: Anonymous | Jan 18, 2016 6:57:12 PM

What boggles my mind is the lack of dna from Teresa Halbach. I remember that being mentioned, and how it just doesn't seem to make sense. Love the blog!

Posted by: Denise Swisher | Jan 19, 2016 8:36:42 AM

The DNA on the key is easily explained: the shed skin cells on the floor/carpet in Avery's room where the detective from Manitowoc 'found' the key, or purely by rubbing the key on any of Steve's items in that room. Dust in any house is partly human skin cells. What is curious is why that key is devoid of anyone else's DNA. It had to have been cleaned before SA's DNA got on it.

The latch DNA could have been put on there at any time. How and when did the authorities get in the car? Did they maybe already have that spare key?

Posted by: JLWhitaker | Jan 19, 2016 3:26:51 PM

Some people keep the spare car key in the car for emergencies (I have a friend who keeps it in his glove box, but some advise using a magnetic box).

Posted by: Anonymous | Jan 20, 2016 7:38:46 AM

Wow. Amazing info Colin. I was unable to understand how SA could be innocent solely because of that "sweat DNA"... I couldn't get past that... and now that too may be a non-issue.
Are you able to comment on the statements made that SA had left a message on Teresa's phone after she'd already been to his property, where he didn't use *67, and asked why she'd never shown up? Not sure what to make of that info...

Posted by: Reagan | Jan 20, 2016 4:21:16 PM

Anonymous: Sure.

Denise: In other words, you would have expected the killer to have left DNA evidence on her?

JLWhitaker: There was the whole issue with the license plate check before her car was officially found, right?

Anonymous: Thanks for the link.

Reagan: I’ll look into it.

Posted by: Colin Miller | Jan 20, 2016 6:37:32 PM

Wheres the purse, and other set of keys

Posted by: Stormy | Jan 21, 2016 7:10:07 PM

Simple on the *67 phone calls. She didn't answer the first few calls and he gave up trying to conceal his identity. If he was leaving a message it would be pretty clear who he was...would it not. No point in disguising the phone number. It is all theoretical anyways and could never be used in the court of law to prove anything. It is circumstantial.

Posted by: Jackie Brown | Jan 22, 2016 10:21:20 PM

"DNA extracted from a man's blood cells is identical to the DNA extracted from his sperm cells." --> Sperm is haploid, it has only 23 chromosomes whilst the other cells in your body have 46 (23 pairs), whilst you can identify that the sperm is a match, I think if you're gonna get technical (and you'd expect that from an expert..) you can't say they're completely identical because they don't even contain the same number of chromosomes. Also wondering can't one morphologically characterise the cells prior to DNA extraction (if cells aren't degraded) - there are many differences in the morphology of cells in our body (even white blood cells have multiple types which all vary morphologically)despite containing the same DNA.

Posted by: Isabel | Jan 25, 2016 12:49:09 PM

One, unless one performs a separate test, one should not speculate as to the tissue or fluid which deposited the DNA. Two, sebum is known as a potential source of touch DNA (“DNA fingerprinting secondary transfer from different skin areas: Morphological and genetic studies, ” doi:10.1016/j.fsigen.2014.03.005). Three, there is DNA in sweat (“Cell free DNA as a component of forensic evidence recovered from touched surfaces” doi:10.1016/j.fsigen.2011.01.004): “n this investigation, the presence of CNAs in sweat was detected on 80% of healthy individuals tested, with an average concentration of 11.5 ng of cell free DNA recovered per mL of cell free sweat. The mechanism for diffusion of CNAs into sweat is currently unknown, but is thought to be analogous to the excretion of other metabolites in sweat through sweat ducts.”

Posted by: Christopher Halkides | Jan 26, 2016 6:26:19 AM

The existence of DNA does not give information on the time or manner of its deposition.

Posted by: Christopher Halkides | Jan 26, 2016 6:47:31 AM

2 points. 1) We've already determined that any DNA evidence presented in this case lacks credibility. If you find 2 samples you strongly suspect to be false, what will you think of the 3rd sample you find? And yet we continue to discuss DNA. 2) Life in prison is not the penalty for being a pervert. So even if he were one, this would have zero relevance. Yet the public continues to discuss possible perversions.

Posted by: Theory Neutral | Jul 16, 2016 4:48:42 AM

The reason DNA samples are collected from buccal mucosa ('cheek scraping') is that oral epithelial cells are nucleated. That is to say, these cells are a rich source of DNA. The skin on the other hand (or elsewhere) does not normally desquamate (shed) nucleated cells. The topmost layer of the epidermis is anucleate,and very little DNA is present. If an individual has dandruff, or a scaly rash then the skin does slough skin cells containing nuclei (and therefore DNA). Sweat does not usually contain cellular material.
With respect, Dr Ann Hunt's testimony about skin is a little misleading.

Scanning electron mIcroscopy of the swabs may reveal cells, and if they were found to be nucleated that would be strong presumptive evidence that they were not of cutaneous origin.

Posted by: Simon | Dec 28, 2018 9:33:40 PM

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