>> I think there are cases where diplomatic immunity has been waived after the fact, by the home country, so that a murder charge can proceed. Ex-Diplomat Gets 7 Years for Death of Teen in Crash - latimes - December 20, 1997 <<
Yes, I remember the case. It was extensively covered in the Wash DC local media. The crime was so bad that the home country (Republic of Georgia) revoked the guy’s diplomatic immunity, after which he definitely became subject to the USA’s jurisdiction.
Don’t remember the outcome, but presumably he went to prison, with the prospect that he’d be deported whenever the prison term ran out.
Or maybe — as can happen — he was sent back to Georgia to serve his prison term in his home country. I guess he’d do OK there if his family had enough dough to bribe the warden and guards. But otherwise, a prison in the USA might be “nicer” so to speak.
Even if his immunity hadn’t been revoked by his home country, you said yourself that a diplomat can be expelled. My point was that this renders the diplomat subject to at least a little bit of US jurisdiction.