On Thursday, Angelo Robinson walked out of an Ohio jail. Mr. Robinson, 43, had spent more than half of his life behind bars and, until quite recently, had no reason to believe he would get out anytime soon.

But a remarkable effort to free him began last year, and eventually both the prosecutor’s office that won his 1997 murder conviction and relatives of the woman he killed supported his release.

No one disputed his guilt. His release on Thursday was achieved through an unusual legal arrangement based on the simple notion that Mr. Robinson had, as one of the victim’s sisters put it, “been punished enough.”

Some criminal justice experts said the very fact of a release like this, however unique, reflected a shift in the debate over mass incarceration. People who were once left completely out of that conversation — those locked up for violent crimes — are now moving, slowly, toward the center of it.