It was pretty much as I figured. They entrapped him.
With all those chemists and biologist they had, it's not too surprising they'd have a shifter poison; probably one they plan to use in this future attack.
I think we've only seen a glimmer of Asa's abilities.
In ancient times, many of the most learned scholars were also herbalists. The use of herbs and spices in foods was not only for flavor, but to prevent food borne pathogens.
Many rapes on reservations go unpunished. Of course murder is another matter, but In his shattered condition Micco wouldn't be a very good witness.
Time and healing changes the equation and there is no statute of limitation on murder or arson.
Or Sam could be collateral damage by someone out to destroy Micco. We still don't know the details behind the attack on his family. Why didn't they kill him outright and what happened to those perps?