The Illinois attorney general's office has opened an in-depth examination of how Cook County prosecutors have handled the trial and nearly two decades of appeals in a controversial 1992 double murder case that sent a teenager to prison for life, even though records showed he was in a Chicago police lockup when the crime occurred, according to court documents and interviews.

At issue is whether prosecutors failed to turn over key information to defense lawyers that would have helped the case of Daniel Taylor, whose defense at trial seemed ironclad: that he had been arrested on unrelated charges before the murders occurred and was not released until after.