Science and law have led to the exoneration of hundreds of criminal defendants in recent decades, but big questions remain: How many other innocent defendants are locked up? How many are wrongly executed?
A new statistical study says about one in 25 people imprisoned under a death sentence is likely innocent.
The study appearing in the Proceedings of the National Academy of Sciences says it is all but certain that at least several of the 1,320 defendants executed since 1977 were innocent.
The study's lead author - Professor Samuel Gross of the University of Michigan law school - says the great majority of innocent people who are sentenced to death are never identified and freed.