A 20-year-old man charged Sunday with shooting two police officers watching over a demonstration outside the Ferguson Police Department had attended a protest there earlier that night but told investigators he wasn't targeting the officers, authorities said.

St. Louis County Prosecutor Robert McCulloch said suspect Jeffrey Williams told authorities he was firing at someone with whom he was in a dispute.

"We're not sure we completely buy that part of it," McCulloch said, adding that there might have been other people in a vehicle Williams is accused of firing from.

Williams is charged with two counts of first-degree assault, one count of firing a weapon from a vehicle and three counts of armed criminal action. McCulloch said the investigation is ongoing.

The police officers were shot early Thursday as a late-night demonstration began to break up following the resignation of Ferguson Police Chief Tom Jackson in the wake of a Justice Department report that found widespread racial bias in the police department.

"He was out there earlier that evening as part of the demonstration," McCulloch said of Williams.

But several activists who've been involved in the protests since the Aug. 9 fatal shooting of 18-year-old Michael Brown by a Ferguson police officer told The Associated Press they were not familiar with Williams.

Williams used a handgun that matches the shell casings at the scene, McCulloch said. He also said tips from the public led to the arrest.

Williams, who St. Louis County Police Chief Jon Belmar said is black, is being held on $300,000 bond. County police spokesman Brian Schellman said he didn't know whether Williams had an attorney or when he'd appear in court. A message left at the St. Louis County Justice Center was not immediately returned.

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