Prosecutor friend in another state just emailed me:
I was told when I started at this job that by the time we catch a rapist in [my state], it was estimated he had raped six times... Curiously, I just handled a case where the rapist (who was walked in on by a roommate in mid-act and fled) was recognized by that roommate a couple of months later when the rapist walked into her rape counseling center in [large urban city] to volunteer as a counselor. They gave him a bottle of water at the rape crisis center as they interviewed him, swapped out the bottle as he toured the facility, then matched his DNA from the bottle with his semen from that rape (one of several he ended up matching for).
I was so proud of that counselor and their cool-headedness... I could kiss them.