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Features

Just a Touch: Using Touch DNA Evidence

With new technology, just a few cells left behind by a perp can help investigators close a case.

December 01, 2008  |  by David Spraggs


Peggy Hettrick was brutally murdered on Feb. 11, 1987. She was stabbed to death then sexually mutilated. The murder rocked the normally peaceful town of Fort Collins, Colo., and it went unsolved for more than a decade. Then in 1998 the Fort Collins Police Department obtained an arrest warrant in the case. Tim Masters, who was 15 at the time of the murder and who had lived about 100 feet from where Peggy's body was found, was convicted of the murder by a jury of his peers in 1999.

But the story doesn't end there. Masters was released from prison, where he had served almost nine years, last January. His release is credited to science.

New forensic DNA technology was used to test evidence from the case. The results raised sufficient doubts that a special prosecutor assigned to the case requested that the judge vacate the murder conviction.

Local newspapers reported that a technique called "touch DNA" was used to analyze the clothing Peggy Hettrick was wearing when her body was found. According to the media, trace amounts of DNA were found on her clothing, and these DNA results led to an alternate suspect, identified as one of Peggy's former boyfriends. At the time this article was written, no other arrests have been made in the case.

I want to make it clear that I have no inside information on this case. I have no idea who killed Peggy Hettrick. I only know what was released to the media.

My interest in this case lies in the development of new forensic technology. The "touch DNA" results created enough reasonable doubt that Masters' murder conviction was overturned.

This goes to show the power of the technology. A minute amount of cells left on the murder victim's clothing in 1987 was powerful enough to raise sufficient doubt in this case. It also has the potential to help detectives like myself close a lot of unsolved cases.

How It Works

Stories about "Touch DNA" are all over the media these days as it was involved in the Tim Masters case and other high-profile cases. It's also on the lips of a lot of police executives wanting their agencies to use the technology. This article will hopefully shed some light on this powerful forensic tool for law enforcement.

"Touch" or "trace" DNA is simply a term used to describe the collection and analysis of microscopic amounts of cellular material. The DNA is assumed to be from epithelial or skin cells. Unlike most other types of genetic material, including blood, saliva, and semen, this genetic material can't be seen with the naked eye.

There's also no presumptive test to indicate whether the cells are present or not. The cells slough off or are transferred from the individual and onto any item. That means the laboratory technician must somehow liberate these cells from the evidence.

Once the cells are removed, they undergo the exact same laboratory procedure as standard DNA testing; it's just that the quantity of DNA needed for analysis has gotten smaller.

If a DNA profile is developed, it's handled like any other profile, being entered into CODIS (Combined Offender DNA Index System) if appropriate and compared against the national DNA database. It is important to note that elimination standards from the victim and possibly the first responder may be needed for comparison purposes to the "touch DNA" sample profile before it is uploaded into the CODIS database.

1.5 Nanograms

According to Angela Williamson, director of forensic casework at Bode Technology Group, the FBI first published a paper on touch DNA in 2001. However Bode, a leading private company offering forensic DNA work to law enforcement, has only been offering "touch DNA" for about three years.

Colorado Bureau of Investigation Laboratory Agent Mary Schleicher indicates that trace DNA technology has evolved from current practices. Advances in both technology and laboratory techniques have allowed results to be validated at lower and lower quantities of DNA. Williamson states that only about 200 to 300 individual cells are necessary for DNA analysis. This is only about 1.5 nanograms of DNA, or just over a billionth of a gram.

Bode Technology Group has validated four different methods for removing the cells from the evidence.

Bode uses either wet or dry swabs, a scraping technique, or a tape lift technique, depending on the nature of the evidence involved. The company's newest technique involves, believe it or not, Post-It notes. Bode has found that the adhesive on a Post-It note is perfect for collecting DNA from sensitive materials like facial tissue, where a normal tape lift would tear the evidence.

Bode is seeing a large increase in the number of "touch DNA" cases being submitted by law enforcement agencies from around the country. Angela Williamson believes this is because the technique has been used in a number of high-profile cases.

Because Bode is a private company, turnaround times are often much faster than overworked, but otherwise excellent, state labs. Bode charges between $995 and $1,095 per sample. You can contact Bode for further information.

Tags: DNA, Forensics, Crime Scene Investigations, Evidence, Cold Cases, Touch DNA

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Comments (1)

Displaying 1 - 1 of 1

neelam @ 10/9/2011 6:51 AM

good work david..
i had some curiorsity about the touch dna technology, which i got to knw from your article. its undoubtedly influential collection of knowledge about this technology. this dna technology has tremendous research aspects. it can be used in various cases like
1. to establich the identity of a person in the cases of unclaimed deceased bodies where we can compare the dna of deceased body with the suspect's belongings.
2. in cases of cyber crimes where the user of a certain laptop or pc can be identified on the basis of this technology.
3. and even we can fix the authorship of the anonymous letters by swabbing the letters for touch dna profiling.
undoubtedly its a good technique to collar the criminals specially in cold cases.
but i wanna to add one thing about the loopholes of this technique as it is mentioned in an eg of a shirt given by u dat the shirt may carry touch dna of wearer as well as the person who might have handled it before its purchase, i think quantitaion of dna can be done for this kind of issues. the quantity of the epithelial tissues sheded from the wearer will obviously in large quantity than the other persons. so i think this problem can be sorted out by this.

from ur article i got my dessertation topic
thnks for that

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