The suspect, Jeffrey L. Williams, has admitted to firing the shots that wounded the officers early on Thursday, said St. Louis County Prosecuting Attorney Robert McCulloch.

The gunfire rang out just after midnight at the end of a rally to call for sweeping reforms in Ferguson, where an unarmed black 18-year-old was shot to death by a white officer last summer.

Michael Brown's death touched off months of protests against law enforcement's treatment of minority groups, in Ferguson and around the country, and led to a U.S. Justice Department probe that found pervasive racial bias on the part of the city's mostly white police force.

Williams was arrested after a massive manhunt, with the help of tips from the public and video evidence, McCulloch told a news conference.

An African American who had been on probation for possession of stolen property, Williams told investigators that he was not targeting police but was shooting at someone else, McCulloch said.

A 41-year-old county police officer suffered a shoulder wound and a 32-year-old from a nearby police department sustained a facial wound in Thursday's shooting. Both were treated and released by a local hospital.

Williams, whose bond was set at $300,000, appears to have fired a .40-caliber handgun from a car, McCulloch said.

A lawyer for Williams could not immediately be reached.

A handgun was recovered in his residence and matched shell casings found at the scene, according to McCulloch, who said that although Williams appeared to be the only shooter, other people may be charged as the investigation continues.

"This arrest sends a clear message that acts of violence against our law enforcement personnel will never be tolerated," U.S. Attorney General Eric Holder said in a statement.

The shootings took place just hours after Ferguson's police chief resigned in the wake of the scathing U.S. Justice Department report. Chief Tom Jackson's resignation followed the departures of the city manager and a municipal judge.

PRE-SHOOTING ROBBERY

The extent to which Williams may have been involved in street demonstrations remains unclear. McCullough said Williams may have participated in protests. Several long-time activists said they did not recognize or know Williams.

One frequent protester, Bishop Derrick Robinson, told local media that he had spoken to Williams early on Sunday and said the shooting had nothing to do with the protests.

Robinson said Williams had told him that he had been robbed earlier that night, and had returned to the area and shot his gun in the air out of frustration.

"He told me that he shouldn't have done it," Robinson told the St. Louis Post-Dispatch. "He was embarrassed. He showed deep remorse. He wishes he could retract things."

News of Sunday's arrest was greeted on the streets of Ferguson with a mix of relief and a sense that the protests would not fade away.

"I just hope they got the right guy, and that he gets what he deserves," said Gussie Klorer, a 60-year-old professor at St Louis University, adding she thought the arrest would have no bearing on the street demonstrations.

"The protests seem to have a life of their own," she said.

But the news also prompted a show of support for Ferguson's beleaguered police force. Dozens of people gathered in front of police headquarters, many of them holding signs reading "We Support the Badge" and "Thank You Police."

There was a brief clash on Sunday between the pro-police demonstrators and about 15 people who converged on them shouting "you support baby killers", while one among them trampled and ripped an American flag.

The two groups met in the middle of the street, face to face, and began shouting at each other, though tensions cooled after the pro-police group disbanded.

The Justice Department report said Ferguson police overwhelmingly arrested and issued traffic citations to black residents to boost city coffers through fines. That helped create a culture of distrust that exploded in August when city police officer Darren Wilson fatally shot Brown.