This is some Buuuuulshit.

[Xrated O.G.]

The agent was breaking the law (failure to maintain lane). He should not be immune from prosecution for negligence. No other profession is.
The agent lied as to the cause of the wreck - again, breaking the law. He should not be immune from prosecution for an intentional lie.
Possession of the vehicle was in the FBI's hands, which means that they should be held responsible for any negligent action on the part of one of their employees, just like every other corporation in the US is.
This is a manipulation of the legal system to exempt one group from the law. It is not for the public good, and is no different that the government corruption that we see in other countries like China, who we publically condemn for thier corrupt policies.