Potential charges against suburban St. Louis police officer who shot, killed Michael Brown

A member of the Missouri National Guard stands guard at a police command post Tuesday, Aug. 19, 2014, in Ferguson, Mo. Ferguson's leaders urged residents Tuesday to stay home after dark to "allow peace to settle in" and pledged several actions to reconnect with the predominantly black community in the St. Louis suburb where the fatal shooting of 18-year-old Michael Brown has sparked nightly clashes between protesters and police. (AP Photo/Jeff Roberson) (The Associated Press)

CHICAGO – A Missouri grand jury could begin hearing evidence as soon as Wednesday to determine whether any charges should be filed against a white suburban police officer who fatally shot unarmed black 18-year-old Michael Brown.

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.

Here's a look at some of the legal issues:

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What state charges could Wilson face?

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 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 in first-degree murder, the second-degree charge doesn't require evidence of premeditation. Two lesser but still-serious charges are voluntarily or involuntary manslaughter, which would follow a finding Wilson acted recklessly or negligently in causing Brown's death.

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How critical is motive?

It's extremely important 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."

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Are there other relevant state laws?

Yes. One is called "defense 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 didn't know Brown was a robbery suspect. Wilson could try to argue the crime Brown was fleeing wasn't the robbery; he could contend the crime was Brown pushing or hitting Wilson.

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What's the role of autopsy results?

Bullet wounds to the back of Brown's body could render incredulous any theory Wilson killed Brown from fear for his life, Joy explains. If all of the bullets entered went through the front of Brown's body at close range, that could support claims Wilson fired in a struggle.

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Could prosecutors opt not to charge Wilson with anything?

Yes, if they conclude he acted in self-defense. But, Joy said, prosecutors do have to account for the fact someone died one way or another. That means it's unlikely they'd 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.

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What charges could federal authorities pursue?

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'd 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. It would hardly be the first time they took such action under the statute, called "Deprivation of Rights Under Color of Law." The Rodney King case was brought under these post-Civil War federal laws protecting civil rights.

And in the first four years of Barack Obama's presidency, the Justice Department brought more than 250 such cases.

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AP writer Pete Yost in Washington contributed to this report.