[mike_d]

> Thus, my understanding is that this would be standard diplomatic immunity, no?

Diplomatic immunity is very nuanced and has multiple levels, but in general being a head of state alone does not qualify you. You need to hold a role within a diplomatic mission to the country in which you committed the crime.

Historically the US justice system has blocked civil suits against foreign states and heads of state out of respect for their sovereignty. The major exemption to this under the FSIA is if the foreign state has a commercial nexus to the United States. The Saudi sovereign wealth fund's multiple investments in the US absolutely pierce the protections they would have had.