I was replying to the OP. If said Erdogan security forces had diplomatic immunity (it doesn't look like they did, but I haven't read the details), and had they bashed heads including killing someone, they could not be prosecuted. It sucks and has meant some horrendous crimes went unprosecuted. But it's a tradeoff and protects our diplomats from false charges.
BTW, just because someone is part of a foreign leader's entourage, I'm not sure that automatically confers diplomatic immunity. It's typically applied to embassy staff.