From time to time, targeted killings (HVTs) have been discussed here and elsewhere. So far as current operations are concerned, the topic is an OpSec mantrap. I've looked at it generally from a legal standpoint. Basically, legality comes down to whether the Laws of War apply and the HVT can be considered a combatant of a power in an armed conflict (kill anytime, anyplace); or whether some form of Law Enforcement rules apply.

I somehow missed downloading the 2009 Crawford JSOU article which Ted posted a month ago - so thanks for the Wiki link reminder. Another decent JSOU article is 2007 Turbiville, JSOU Report 07-6 Hunting Leadership Targets, linked above a couple of years ago.