Jeffrey Williams is pictured in this undated booking photo provided by the St. Louis County Police Department.

He added that Williams, who is being held at a local jail on a bond of $300,000, used a 40mm handgun, matching shell casings at the scene. Williams, a north St. Louis County resident, was on probation in St. Louis County for receiving stolen property at the time of Thursday's incident, McCulloch said.

The suspect reportedly told police that he had been shooting at someone else at the time of the incident and only accidentally struck the police. McCulloch added that authorities have yet to determine whether Williams was in fact aiming at someone other than the police.

"We're not completely sure we buy that part," he said.

Part of the investigation will involve determining whether other people should also be criminally charged, though McCulloch said "it appears there is only one person firing shots."

McCulloch said the investigation was aided in part by community members who stepped forward and provided information to the police.

"What got the police to this point is information that was provided to them by members of the community," he said.

The officers were shot early Thursday as a crowd began to break up after a late-night demonstration. That protest unfolded after Ferguson police chief Tom Jackson resigned in the wake of the scathing federal Justice Department report, which found widespread racial bias in the city's policing and in a municipal court system driven by profit extracted from mostly black and low-income residents.

A 41-year-old St. Louis County officer was shot in the right shoulder, the bullet exiting through his back. A 32-year-old officer from Webster Groves was wearing a riot helmet with the face shield up. He was shot in the right cheek, just below the eye, and the bullet lodged behind his ear.

The officers were released from the hospital Thursday. But St. Louis County Police Chief Jon Belmar said Thursday they could have easily been killed and called the attack "an ambush."

Attorney General Eric Holder said in a statement Sunday that the arrest "sends a clear message that acts of violence against our law enforcement personnel will never be tolerated" and praised "significant cooperation between federal authorities and the St. Louis County Police Department."

The shots were believed to come from a handgun across the street from the police department, which has been a national focal point since the fatal Aug. 9 shooting of Michael Brown, who was black and unarmed, by now-former police officer Darren Wilson. Wilson was cleared by the Justice Department's report and by a county grand jury led by McCulloch.

The federal report found widespread racial bias in the city's policing and in a municipal court system driven by profit extracted from mostly black and low-income residents.

Al Jazeera and The Associated Press