Federal courts have sometimes blocked state prosecutions under that provision, out of concern that state authorities are using their prosecutorial power to frustrate the federal government from legitimately exercising its own powers, according to Bryna Godar, a staff attorney at the University of Wisconsin Law School’s State Democracy Research Initiative.

Godar wrote in the Lawfare legal publication that federal courts have repeatedly blocked state prosecutions when the federal official was reasonably carrying out lawful federal duties. But, outside those circumstances, courts have allowed the prosecutions to go forward.

“In many cases, the federal officer may ultimately walk away with immunity. But not always,” Godar wrote.

Another potential challenge is courts disagreeing on the exact contours of this type of immunity for federal officers, leaving the law in this area somewhat unsettled, according to Godar. The U.S. Supreme Court hasn’t weighed in on this type of immunity in more than a century.

Murder and manslaughter charges could be in play

Even if state officials do decide charges are warranted, they are unlikely to bring a first-degree murder charge, according to Rahmani. That crime generally requires premeditation.

He said state officials might consider a form of manslaughter or a lesser murder charge, which come with maximum penalties ranging from 10 to 40 years in prison. For example, a person can be guilty of second-degree manslaughter in Minnesota by unreasonably endangering a person’s life or of second-degree murder by intentionally killing someone without premeditation.

“It’s possible that there’s multiple charges and they don’t just land on one, to give jurors really the option,” Rahmani said.

‘Very tough job for prosecutors’

If the ICE agent ended up facing charges, he would likely argue he shot Good in self-defense, former prosecutors told USA TODAY.

Minnesota law allows officers to use deadly force if it’s reasonable for them to believe the force will protect them or another person from great bodily harm.

In this case, the agent may argue that Good appeared to be directing her SUV at him. Trump officials have highlighted video footage from the front of the SUV, saying it shows movement in the agent’s direction. Advocates for Good have pointed to footage from the rear, which shows the vehicle turning as if to pass the agent and get away.

Looking across multiple public videos, which show both Good’s handling of the wheel and the movement of the SUV’s tires, Good is driving simultaneously rightward and forward, as the agent stands towards the left, front side of her car. Then there are three brief sounds that may be bullet shots, one as the agent points his gun at the left side of the front windshield, and then two more as he is pointing at the side window as the car drives away.

Protests have mounted across the country, with many arguing the video shows the shots weren’t reasonable, and protesting what they see as ICE’s aggressive behavior — including towards U.S. citizens such as Good — more generally.

“They are already trying to spin this as an action of self-defense,” Minneapolis Mayor Jacob Frey said at his Jan. 7 press conference. “Having seen the video myself, I want to tell everybody directly – that is bull—-.”

But Bederow said, as emotional as the case is, there is much more to be parsed out in terms of witness interviews and video analysis that could illuminate key legal questions, such as whether it was reasonable for the ICE agent to believe he was in danger.

“Lawyers who do this for a living and have experience in self-defense or justification cases realize that there’s a lot more nuance to this than saying, ‘She didn’t mow the guy down, and he shot and killed her,’” Bederow said.

If he does face charges, the agent might argue that he was operating in a heated environment — he and Good’s wife were filming each other outside the SUV as she asked if he “wanted to come at” them, just seconds before the shooting — and that he didn’t have the luxury of analyzing the direction of the SUV’s movements in a frame-by-frame, slow motion video.

“It’s going to be a very, very tough job for prosecutors, notwithstanding the fact that there is very disturbing video and a woman lost her life,” he said.