The part I have trouble with, as a former cop, is the alteration of evidence. That action speaks to a consciousness of guilt that argues against granting any form of amnesty.
I understand that part of it, I have to go back and review some of the accounts as I also seem to recall that the perp had turned and the agents thought they saw him reaching for or holding an object (isn't that what most if not they all say?), I could be wrong on that, but I hear ya on the evidence tampering part as well.