S6·E60 Watch My Lips

Jim Carver is assaulted while trying to question a suspect - James Doyle - who is later revealed to be deaf. He firmly believes in his intial instinct that Doyle is a villian, and believes that he shouldn't get any special treatment. In the end, however, he changes his mind - only to discover that James Doyle is not James Doyle - and that his initial instinct was right. [Source: jimsgirl]