DNA Evidence Exonerates Man Convicted of Murder
DNA Evidence Exonerates Man Convicted of Murder .
The Innocence Project has struck again. This time Christopher Abernathy, found guilty of the 1984 murder of a 15 year old girl in Illinois has had his case dismissed after he has served 30 years. Mr. Abernathy went into custody as a 19 year old man but he has been exonerated by DNA evidence:
In 1984 when this crime occurred, if the woman was also sexually assaulted, or if there was evidence under the fingernails, forensic units would obtain samples from the scene and the victim. If a sexual assault was involved, there would be samples from the woman’s vagina, which may have yielded sperm of the attacker. If the woman fought back by scratching her attacker, she may have had skin and blood cells under her fingernails. This all would have been preserved at an autopsy.
In 1984, DNA evidence was not allowed in court as reliable. The first method that was used to extract and compare DNA samples was called the “RFLP” method. This method resulted in the bar-code looking data that one sees on “CSI”-type TV crime dramas. But the RFLP method required a rich source of DNA since that method required a large sample.
Shortly after DNA was accepted as an accurate scientific method in court in the early 1990’s, the currently-used “STR” method meaning short tandem repeats replaced the RFLP method. Only a very small sample is necessary for the STR method because the equipment used “copies” the genetic code. Now even smaller amounts are needed than when STR came into existence. this is often referred to a “touch DNA” where a few skin cells may be deposited on another surface such as a fear shift or steering wheel in a car.
If DNA is stored appropriately, it may not degrade. Exposure to heat and of course bleach destroys it. Apparently in Mr Christopher Abernathy’s case, the samples from 1984 were apparently still in existence. Many states allow a re-testing with modern methods and this has resulted in the exoneration of people such as Christopher Abernathy.
When the reporters say that the DNA sample found is not consistent with his, this would mean that there was a sample from a suspect left at the scene or on the body. It also means that at at least one of the normally checked 15 alleles, there was a DNA value that is inconsistent with Mr. Abernathy’s. This is somewhat complex and tedious to explain, but the bottom line is that if one single allele is different between Mr. Abernathy’s DNA and that of the presumed attacker, that DNA cannot belong to Mr. Abernathy. There is usually more than one allele that is different, and the forensic scientists simply state that the DNA “excludes” Mr. Abernathy as a contributor to the forensic sample.