The honest answer: Nobody knows.
A recent article in the New York Times asks a question often heard by the Innocence Project: How many people convicted in the United States are innocent?
Observers from across the criminal justice system have weighed in.
Samuel Gross, a law professor at the University of Michigan, has found the rate of wrongful conviction in death row cases to be somewhere between 2.3 and 5 percent.
A recent review of biological evidence in 31 randomly chosen Virginia cases led to DNA testing that could yield results in 22 cases, two of which resulted in exonerations –- a small sample size but an indicator that the rate could be as high as 9 percent.
A couple of years ago, Supreme Court Justice Antonin Scalia cited questionable and discredited calculations from Oregon Prosecutor Joshua Marquis (who divided the number of DNA exonerations by the total number of felony convictions) to make his claim that the wrongful conviction rate is .027 percent. As Gross points in a recent law review article: "By this logic, we could estimate the proportion of baseball players who’ve used steroids by dividing the number of major league players who've been caught by the total of all baseball players at all levels: major league, minor league, semipro, college and Little League -- and maybe throwing in football and basketball players as well."
The Times article notes that while there is disagreement about which calculations might help suggest the magnitude of the problem, there is a consensus that nobody really knows how many innocent people are in prison –- and we may never know.
The Innocence Project has always said that DNA exonerations are just the tip of the iceberg, since only 5-10% of all criminal cases involve biological evidence that can be subjected to DNA testing (and even in those cases, the evidence is often lost, destroyed or too degraded to yield results in DNA testing). But the 215 wrongful convictions overturned to date by DNA testing illustrate the broader causes of wrongful conviction and show the need for reforms that can prevent injustice. As the Times article says:
"… A few general lessons can be drawn nonetheless. Black men are more likely to be falsely convicted of rape than are white men, particularly if the victim is white. Juveniles are more likely to confess falsely to murder. Exonerated defendants are less likely to have serious criminal records. People who maintain their innocence are more likely to be innocent. The longer it takes to solve a crime, the more likely the defendant is not guilty."
Read the full article here.