Well, the country from which the offender has legitimate diplomatic immunity must waive that immunity for prosecution here to proceed. Unfortunately, that rarely happens, especially with senior-level officials and their families. What typically happens in the case of serious charges (like vehicular homicide or manslaughter) is that the offender is expelled. There was a famous case in the DC suburbs a number of years ago where a diplomat was involved in a series of auto accidents, culminating in a crash in which someone was killed. He was finally expelled from the US, not prosecuted here, because his home country would not waive immunity.
“Well, the country from which the offender has legitimate diplomatic immunity must waive that immunity for prosecution here to proceed.”
Sure, but I’m not worried about prosecuting him for crimes committed while he had immunity. We should just unilaterally revoke his immunity, before he does something we really would like to prosecute him for.
In 1997, Gueorgui Makharadze, formerly the second-highest-ranking diplomat at the Georgian Embassy in Washington, had his diplomatic immunity waived after he killed a Maryland teenager in a drunk driving accident.
It's the exception. Waiver of immunity that is.