That's pretty much what happened to the survivors.
They were acquited of murder charges, but convicted on weapons charges. The Jury thought they were letting them off lightly, but the judge sentenced them to 80 years.
L
The federal government CANNOT allow its agents to be killed without drastic consequences to the killer, regardless of how justified the circumstances. The federal government CANNOT allow its agents (like Lon Horiuchi) to be prosecuted for "following orders".
To do otherwise would be to risk agents refusing to follow orders if they had doubts of their legality, or to refuse to undertake an operation if they felt the personal risk was too high.
The downside of hiring thugs as your enforcers is that a large percentage of them, while willing to commit atrocities to further their careers, are cowards when it comes to facing personal risk