Advocates are sifting through 20 old criminal cases for hints of wrongful convictions in a North Carolina community where a prosecutor once tried to railroad three Duke lacrosse players for rape and where a longtime prisoner was freed after a judge ruled DNA evidence cleared him of rape and murder.

Durham County District Attorney Roger Echols said Thursday he'll cooperate with investigating any innocence claims or questionable prosecutions pointed out by the nonprofit North Carolina Center on Actual Innocence.

Echols and the center's executive director Chris Mumma agreed two years ago that they should investigate whether more cases of possible prosecutorial conduct remained unearthed. The innocence center has been quietly culling down the hundreds of Durham cases that put people behind bars who remain there.