This story was updated at 10:40 p.m. EST.

A white Alabama police officer faces murder charges for the fatal shooting of an unarmed black man, authorities said on Wednesday.

Montgomery police officer Aaron “A.C.” Smith, 23, is free on $150,000 bond after investigators found that he broke the law when he shot and killed Gregory Gunn last Thursday, Montgomery County District Attorney Daryl Bailey said.

The case now goes to a grand jury, he said.

Police killings of African-Americans, many of them unarmed, have sparked repeated protests over excessive use of force in the past few years.

An attorney for Smith told a reporter for the Montgomery Advertiser newspaper that the officer had stopped Gunn and started to search him “for his own safety” when Gunn broke from him and ran, according to an interview posted on the reporter's Twitter feed.

The attorney, Mickey McDermott, told the newspaper that Smith tried six times to use non-lethal force, including using his Taser and baton, to subdue Gunn, but that Gunn picked up a weapon and Smith had to use deadly force “as he was trained.”

McDermott could not be reached by Reuters on Wednesday.

In remarks to reporters earlier Wednesday, Montgomery Police Chief Ernest Finley declined to confirm initial reports that Gunn had brandished a stick-like weapon.

“It's possible,” Finley said. “At the end of the day, we're going to wait for the entire report from the DA's office or the SBI [State Bureau of Investigation].”

Mayor Todd Strange said he was not aware if there is any video of the incident.

Strange said the police department, composed of about 500 officers and 45 percent black, has made big strides in community relations over the years and will continue to reach out to citizens in the wake of the shooting.

"We have bridges to build again, but let's don't tear down what we have done," Strange said.

In front of the family home in Montgomery, a woman identified as Gunn's mother spoke to reporters.

"God is still in charge. And heaven knows what happened," she said in a video posted by the Montgomery Advertiser newspaper. "Man may not know. Only one that did it and one that got done to. But heaven knows."