There has been a recent incident relating to a person with diplomatic immunity (a US citizen) being involved in a fatal car crash in the UK. My question is born out of reading about this case, but I'm looking for a general answer; what should happen in every case, not what will happen in this case.
From what I've read a person is only able to receive diplomatic immunity if they are in the foreign nation, and therefore any immunity ends when the person returns home. Does that mean once the person has returned home they can then be held accountable for their actions while in a foreign nation? If so who exactly can hold the person accountable? If the crime wasn't committed in the home nation then their government presumably has no jurisdiction and/or no way to investigate the crime. But if the foreign nation is able to pursue the individual once they have returned home it feels like it short-circuits the entire principal of diplomatic immunity.