inmate john robb has spent more than half of his life in prison. >> i don't have much hair to comb anymore. >> decades behind bars have made him guarded when it comes to revealing his past, but today that's about to change. >> when the chaplain goes on vacation, the chaplain aides rotate. i like helping them out, sharing with them. >> this convicted murderer is filling in as preacher. friend and therapy group member jack mcgarey comes along for support. >> i've known jack for at least 12 years. he was in the same prison in san quentin in the '80s, which that wasn't a nice place. >> in those days in that prison,