Q: What if a police officer shoots an undercover FBI agent thinking it's an armed criminal?

A: This is a complex legal situation involving the use of deadly force by a police officer against an undercover FBI agent. The key factors would be whether the officer's actions were reasonable given the circumstances and information available to them at the time.

In general, police officers are permitted to use deadly force if they reasonably believe it is necessary to protect themselves or others from imminent threat of death or serious bodily injury. The officer would likely argue that they believed both fleeing individuals posed a lethal threat since they were armed, had just fled the scene of a shooting, and the alleged FBI agent failed to comply with orders to drop his weapon.

However, the fact that the agent identified himself as FBI could potentially undermine the reasonableness of the officer's actions, especially if the agent's shouts were clearly audible. The agent's family would likely argue that the officer acted recklessly by not giving the agent a chance to prove his law enforcement status before resorting to lethal force.

Ultimately, the specific details of the case would be critical - e.g. the exact positioning and actions of those involved, lighting and visibility, how clearly the agent identified himself, etc. Witness testimony and any available video evidence would play a key role.

In terms of precedent, there have been cases of police officers shooting undercover officers and facing legal consequences:

- In 2009, BART police officer Johannes Mehserle shot and killed Oscar Grant, who was actually an undercover officer. Mehserle was charged with murder but convicted of involuntary manslaughter.

- In 1994, NYPD officer Peter Del-Debbio shot and injured an undercover transit officer. He was convicted of second degree assault.

However, each case depends heavily on its particular facts. In a somewhat similar case in 2016, an NYPD sergeant shot and killed a mentally ill woman who charged at him with a bat, and he was acquitted of murder charges, with the court finding his actions reasonable given the apparent threat.

So in summary, it's a difficult case that would hinge on whether the totality of circumstances supported the reasonableness of the officer's split-second decision to use lethal force. Both sides would have arguments, and the outcome would depend heavily on the specific evidence and how compellingly each side could present their case to the court. Consulting with an attorney specializing in police use-of-force cases would be advisable for a more definitive legal analysis.