Do you think the blonde kid (spoilers)

There likely was no murder weapon with his prints on it. Eventually the PD needed to bring both Reiman--which they had done-- and the blond in for questioning and get one to crack.
No gun-knife-club? would be a problem. You would have to indict based on circumstantial evidence and the testimony of a really bad guy.

Bottom line is a murder conviction would probably be difficult even if the blond had priors for assault. They would probably offer a deal if he'd plead to manslaughter.

Kisskiss, Bangbang

I think you brought up a key point about American Gigolo which somehow got swept aside.

It's not a conventional mystery; so the main point of the movie is NOT to figure out who did the actual crime. The main point is whether either of the two leads, Julian or Michelle, is willing to make a sacrifice out of love to save the other.

Julian has several scenes at the end where he is in prison, and they tell him he needs an alibi. The camera lingers on his face, but he says nothing. That's his moral test. He wants Michelle to go back to her mansion and her husband and her life of security; he does not want her dragged into a scandal.

Michelle, however, does not want Julian to rot in jail when she is his alibi. She loves him, so she confesses to the cops that he was with her the night of the murder.

Did the blond guy kill Ms. Rheiman? Did he do it alone, or did Leon help? All I knew at the end was that the blond kid was Julian's replacement in Leon's stable of MAN-WHORES.

Also, it's not just about making a sacrifice and being noble; it's about accepting someone else's love. That's the meaning behind Julian's cryptic line, uttered at the end of the movie.