The number of false convictions is startling, and even now underreported.  Most of these defendants have no-one to advocate for them.  When convictions are reversed, it is often -- even usually -- because of DNA evidence; but in many cases, there simply is no DNA evidence.  Another difficulty arises from the phenomenon of plea bargaining: with the specter of the death penalty looming, it is not difficult to see how a frightened defendant might choose to plead guilty to a crime he (or she) did not commit.  If it's difficult to overturn a conviction that was reached at trial, it's all the more difficult to overturn one that came as a result of a plea.  And you name a very important part of the problem: prosecutors are loathe to admit a mistake, even of a predecessor.  We need an incentive to move prosecutors to do the right thing when the evidence points to a false conviction.  The system is badly flawed.