The rules are bilateral, Reaper. It would depend on their exact status in the U.S. If they are a diplomatic agent assigned to an Embassy here in the U.S., then they will probably have full diplomatic immunity and can be expelled but not prosecuted. Their mission, however, can waive that immunity since it belongs to the mission and not the person (same for U.S. personnel overseas). They can also be tried by their own government once they return home.
And the same would apply to this guy...IF he met those parameters.
Here is an explanation, for U.S. LE officers as they apply to foreign diplomats here. Reverse them and the same is generally true for U.S. personnel overseas, depending on the bilateral agreement (I'm not at work so I can't pull up the official stuff for us). It explains the differences between diplomatic and consular immunities, as well as how just holding a diplomatic passport (and even a diplomatic visa) does not mean you are entitled to full or any immunity. And also how those who are on temporary official duty to a mission do not enjoy ANY immunity.
http://www.state.gov/documents/organization/150546.pdf
Peregrino--yes, he's going to need alot of luck and alot of cooperation. Funny thing is, we enjoyed a good relationship with the locals in Lahore. That's been shot to hell now.