DNA analysis has helped exonerate dozens of people who had confessed to violent crimes. But against Juan Rivera, as detailed in this New York Times piece, prosecutors used new and novel theories to explain away the scientific evidence. How did they do that?

Some interesting facts about DNA evidence:

In the years before DNA evidence was introduced to the legal system, little was known about the extent of wrongful convictions and the situations in which they occurred. That changed in 1986, when an English scientist used DNA testing to help exonerate a man accused of raping and killing two teenage girls (the evidence also led the police to the real killer). Since then, DNA testing has helped exonerate 280 convicted felons in the United States and has exposed deep flaws in our legal system, including misconduct by the police and prosecutors and egregious mistakes made by witnesses and forensic scientists. In his 2011 book, “Convicting the Innocent,” Brandon Garrett, a law professor at the University of Virginia, examined most of the case files for the first 250 DNA exonerations. Garrett found that 76 percent of wrongly convicted prisoners were misidentified by a witness and half the cases involved flawed forensic evidence. The testimony of an informant, often a jailhouse cellmate of the accused, was pivotal in 21 percent of the cases. Perhaps most surprising, 16 percent — virtually all of whom were subjected to interrogations lasting several hours and, in many cases, days — confessed to crimes they didn’t commit. Garrett pointed out another, striking detail in the false confessions: in 38 of 40 false confessions, the authorities said defendants provided details that could be known only by the actual criminal or the investigators, thus corroborating their own admissions of guilt by revealing secret information about the crime that could only have been provided by them.