What does the police officer do after saying good night to the man in the doorway?

After the police officer has said good night to Bob, the man waiting outside the hardware store, he continues pounding the beat. All very normal, we might think. Certainly, that's how 'Silky' Bob feels. But that's not all the police officer did. Judging by what happens right at the end of the story, the officer must also have written a note to Bob and handed it to a plain-clothes detective. The police officer is none other than Jimmy Wells, Bob's old friend from all those years ago, and the man for whom he was waiting outside the hardware store.
As an officer of the law, Jimmy does his duty. But he must still retain some feelings of friendship towards Bob. That's why he can't arrest Bob himself and has to get a plain-clothes detective to do it instead.