CHICAGO (AP) — A Missouri grand jury could begin hearing evidence as soon as Wednesday to determine whether any charges should be filed against the white suburban police officer who fatally shot unarmed 18-year-old Michael Brown.A look at some of the legal issues:What state charges could Wilson face?How important is motive?Are there other relevant state laws?What about the autopsy results?Could prosecutors opt not to charge Wilson with anything?Has the state prosecutor ever undertaken a case such as this before?What charges could federal authorities pursue?

State prosecutors are wading through contradictory narratives as they decide which account to present. Federal authorities also could take legal action against officer Darren Wilson, especially if they decide their state counterparts are drawing the wrong conclusions.

Although the stiffest possible charge is first-degree murder, which can carry the death penalty, legal experts say that’s highly unlikely. It would require proof that Wilson plotted to kill Brown, said Peter Joy, a law professor at Washington University in St. Louis. “It’d have to be a cold and deliberate killing — almost execution style,” he said.

If Wilson is charged, a more likely option could be second-degree murder, which is often applied to killings that occur after someone hastily draws a knife in the heat of a fight. Unlike first-degree murder, the second-degree charge does not require evidence of premeditation. Two lesser but still-serious charges are voluntary or involuntary manslaughter, which would follow a finding Wilson acted recklessly or negligently in causing Brown’s death.

It’s critical to the case. Prosecutors essentially have to get inside Wilson’s head, said Anders Walker, a professor at Saint Louis University School of Law. Did he fire in a fit of racially charged anger, perhaps subjecting him to second-degree murder? “They have to decide what the officer was thinking,” Walker said. “A lot hinges on that.”

Yes. One is called “defence of justification law,” which provides some legal leeway for officers to shoot suspects they believe are fleeing a serious crime and refusing to surrender, Joy said. In this case, some witnesses say Brown was surrendering. And police have said Wilson did not know Brown was a robbery suspect. Wilson could try to argue that Brown was not fleeing the robbery but instead fleeing from the crime of pushing or hitting Wilson.

Bullet wounds to the back of Brown’s body could discredit any theory Wilson killed Brown out of fear for his life, Joy explained. If all of the bullets went through the front of Brown’s body at close range, that could support claims Wilson fired in a struggle.

Yes, if they conclude he acted in self-defence. But, Joy said, prosecutors do have to account for the fact that someone died one way or another. That means it’s unlikely they would decide on a relatively minor charge, such as assault. “It’s likely you’re going to have the state charge him with murder or manslaughter – or nothing at all,” Joy said.

The St Louis County prosecutor overseeing the case, Bob McCulloch, also oversaw a 2000 case in which two undercover officers fired 21 shots into a vehicle, killing two black men during an attempted drug arrest. No weapons were found in the car. McCulloch chose not to charge the officers and a federal report later concluded that the officers fired “out of fear and panic.”

Bringing a murder charge isn’t among their options. They could charge Wilson with a criminal civil rights violation, which carries a maximum life sentence, said Joel Bertocchi, a former federal prosecutor in Chicago. They would have to show Wilson, perhaps out of racial bias, deprived Brown of his civil rights by killing him.

It could take months or even a year for the feds to decide, said Samuel Bagenstos, a former Justice Department official. Any case would probably be based on a set of post-Civil War federal laws protecting civil rights. They formed the basis of the Rodney King case.

In the first four years of Barack Obama’s presidency, the Justice Department brought more than 250 such cases.