Prisons are full of men and women who say they are innocent, and a new effort is underway in Philadelphia to help exonerate some who actually are.

The first DNA-based exoneration took place in 1989 and one of the aims of the newly-formed Pennsylvania Innocence Project is to bring more of that to bear in local cases.

Project co-founder, lawyer David Rudovsky says various similar efforts have freed more than 230 wrongly convicted people nationwide. That's revealed a pattern:

"In 75 to 80% of all cases, in which innocent persons have been exonerated, they were convicted at least in part by eyewitness testimony and that can lead us to come up with better methods of obtaining and presenting eyewitness testimony."