Betting on DNA

“Only a one in 37 million chance of having caught the wrong guy seemed to the police a safe bet.  The problem is that Raymond Easton’s chance of being innocent was not one in 37 million – but only one in thirty-seven.” (Weinberg, 219)

I think this quote displays how the results of DNA can differ greatly depending on what you are looking for.  In the burglary case involving Raymond Easton that was briefly mentioned, police believed they had a solid match for the DNA found at the crime scene.  The tests they ran matched Easton completely, giving them a 1 in 37 million chance that they had the wrong guy.  But, Easton would not admit to the crime.  He was an old man, living much too far away from the crime scene and suffering from Parkinson’s disease.  He could barely get out of his wheelchair, much less drive hundreds of miles to commit a robbery.  The odds the police had the wrong man were actually much, much smaller than they had originally anticipated.  The six loci that were tested did not give the police a 1 in 37 million chance like they had believed, but a 1 in 37 chance.  The original DNA tested had led them to the wrong man, leading me to believe that DNA might not be as concrete a form of evidence as people are led to believe.

Quote

STRs

“I was 99 percent sure it was him,” says Laura Helig…But I had heard about this new technology, STRs…I knew they could give us results on really tiny samples (Weinberg 216).

This new form of analyzing DNA emerged in 1999 and was exactly what Helig needed to catch Helena Greenwood’s killer. Short Tandem Repeats could not only be used on small amounts of DNA but could also give specificity. This article goes into detail about STR testing. Essentially the labs like SERI that worked on Fredini’s DNA analyzed the 6-loci tandem repeats and they matched the DNA found under Helena’s fingernails, which had been stored in evidence since the attack, almost a decade earlier. STR analysis was able to use the small amount of very old DNA found under Helena’s fingernails and match it to Frediani’s DNA which was kept in a DOJ freezer because he was a sex offender. This was the beginning of databases like CODIS that emerged in 1998 to catch criminals even easier then with just STR.

STRs