An improved method of indexing DNA is sweeping law enforcement agencies across the nation and will come into play in Juneau as the prosecution prepares for a murder trial.
The method is Short Tandem Repeat typing, or STR, said Abi Chidambaram, a criminologist and DNA analyst with the state crime lab in Anchorage. The process allows near-perfect DNA analysis using a single cell from a variety of bodily fluids, instead of requiring a relatively large blood sample.
``Usually what the defense will ask is, `What is the chance that someone else on the planet has this profile?' '' Chidambaram said. ``With this new method, the chance is one in quintillions. So the chance of identifying a particular person is pretty high.''
Assistant District Attorney Sue McLean has asked for permission to use this more discriminating method of DNA analysis in the trial of Ronald E. Smith, 33, and Rey Joel Soto, 20. Each is charged with second-degree murder in the beating death of Kenneth Thomas in January near Willoughby Avenue. Trial is scheduled for July 10.
McLean declined comment about prosecution strategy, but court records show Smith's jacket, shoes and pants appeared to be smeared with blood, and police also observed blood on Soto's jacket, shoes and pants. A baseball bat seized as evidence was also smeared. A $5 bill in Soto's pocket also seemed to be bloodstained.
STR technology uses polymerase chain reaction, a sequence which has been around since the early '80s, and applies it to the field of DNA analysis, Chidambaram said. ``The chain reaction is like photocopying DNA.''
Being able to ``photocopy'' the material makes it possible to turn a minute amount of the material into a larger sample. ``In the past, we needed a lot of material,'' Chidambaram said. ``Now we can just take a swab from the inside of the mouth. If we have one cell, we can multiply it.''
Another factor contributing to the efficiency of the Short Tandem Repeat method is that it does not require blood.
Until recently, laboratories required blood samples to isolate DNA, but the state of the science is such now that ``any kind of body fluid that might contain cells'' is a good source, said Chris Beheim, supervisor of the controlled substances section of the crime lab.
Saliva, seminal stains from sheets or underclothes, and even ``tissue from the end of a single hair'' are all potential sources, Beheim said.
Police once turned in a piece of fruit bitten by a suspect, Chidambaram said, and a lab was able to recover sufficient saliva from the bite that they could link it to a person. ``As long as the sample has cells that have a nucleus, you have a starting point for DNA analysis,'' she added.
The icing on the DNA analysis cake is ``new markers are much more discriminating than they were in the mid-90s,'' said Chidambaram, who mastered STR in March.
The new technology is pretty much standardized now across the U.S., Beheim said. ``In the past one lab would be doing one thing and another lab something else, and you couldn't compare results. The FBI and other law-enforcement agencies got together to standardize 13 genetic markers.'' This makes it possible for agencies to share analyses and match suspects, he said.
These particular 13 markers were chosen because they are highly variable, Chidambaram said. ``Each marker or allele is different, and there are eight to 10 variations of DNA at each site. So you look at all 13, and you come up with a genetic profile.''
With the old method, you might be able to narrow down suspects to one in 20. With the new, more specific method, ``we can narrow it down to approximately one in 2,000,'' she said.
``What makes it so powerful is that we are looking at 13 markers,'' Beheim said, ``and each one has its own level of randomness. They act independently of one another; by the time you have 13 lines up, it's irrefutable.''
The accuracy of the method is bad news for bad guys. However, it's very good news for the innocent, because exclusion is usually 100 percent, Chidambaram said. She mentioned the impact of Short Random Repeat typing on The Innocence Project, a nationwide effort to test DNA from old cases. ``If it doesn't match at even one of the 13 sites, you have an exclusion'' -- perhaps of a person previously convicted, she said.
DNA identification is so new that Alaska statutes did not deal with it until 1995, in a law that went into effect Jan. 1, 1996. That statute established a DNA identification registration system. It allows the Department of Public Safety to collect a sample from any person convicted of a crime against another person, and any minor 16 or older who commits a crime that, if he were an adult, would be considered a crime against a person.
Crimes against another person include homicide and sexual assault, Beheim explained. The statute makes the registration system confidential so the information contained in it may not be accessed by the public.
Short Tandem Repeat does not allow labs to access information such as whether people have susceptibility to cancer, Beheim said. ``And it's illegal to use this method for anything but law enforcement -- not for insurance, or job applications.''
The registration system stores DNA analyses by code numbers only, he added, not by names.
CODIS or Combined DNA Index System is the name for the integrated local, state and national law enforcement system of DNA records. The Web site of the Michigan Department of State Police calls forensic DNA profiling technology ``perhaps the most significant law enforcement tool developed since the introduction of fingerprinting.'' In Michigan, new legislation allowed the collection of DNA samples from both convicted and paroled sex offenders beginning in September 1995. About 2,100 samples are now in the data bank.
``Ultimately, CODIS will link all local and state law enforcement agencies, through their crime labs, to a national system for the sharing of DNA profiles as investigative leads. CODIS promises to be a powerful new tool for the investigation of violent and serial crimes,'' Michigan DSP's Web site states.
© 2017. All Rights Reserved. | Contact Us