My guess is that, to a person on the verge of stealing such an artifact, whether there is a policy of no investigation on safe return is near the last thing on

My guess is that, to a person on the verge of stealing such an artifact, whether there is a policy of no investigation on safe return is near the last thing on their mind. A person acting on impulse isn't putting much effort at all into thinking it through, and the motivations and attention of someone who has planned the heist in advance are all focused in the opposite direction - they have already chosen on an action in which return plays no part. Therefore, I would lean towards there being no investigation, or at least no public investigation. The much trickier problem, not uncommon in art theft, is when the thief attempts to ransom the artifact.