Reuters – Police hunted for a second day on Friday for suspects in the shooting of two police officers at a protest rally in Ferguson, Missouri, after U.S. President Barack Obama said those responsible must be brought to justice.

The officers were shot and wounded as a demonstration in the St. Louis suburb was breaking up around midnight on Thursday morning, driving up tensions in a community that has become the center of an intense nationwide debate over race and policing.

Investigators scoured streets near the scene of the shooting for clues and several people were brought in for questioning. They were all later released and there have been no arrests, police said.

The shooting happened just hours after Ferguson's police chief resigned following a U.S. Justice Department report that said deep-rooted racial bias in the city's mostly white police force had created a "toxic environment" in the predominantly-black community.

The protesters at the Ferguson rally had been demanding police reforms. Obama, the United States' first black president, said such protests were warranted in the light of events in the city, but said criminal acts could not be justified.

"What had been happening in Ferguson was oppressive and objectionable and was worthy of protest," he said during an appearance on the ABC program "Jimmy Kimmel Live".

"But there was no excuse for criminal acts, and whoever fired those shots shouldn't detract from the issue. They're criminals. They need to be arrested," Obama said.

The scene of the shooting has been the site of regular demonstrations since the fatal shooting in August of an unarmed black 18-year-old Michael Brown by a white policeman.

That killing triggered protests around the country and prompted the Justice Department investigation as well as a contentious national discussion over the use of deadly force by police officers.

Condemning the wounding of the officers, activists held a candle-light prayer vigil for peace late on Thursday. About 100 people then held a boisterous but peaceful protest outside the police station under light rain.

The crowd blocked traffic at times, but there were no arrests and the demonstration passed without incident.

In Thursday's shooting, a 41-year-old St. Louis County police officer suffered a shoulder wound and a 32-year-old colleague from the nearby Webster Groves Police Department got a bullet lodged near his ear.

Crime Stoppers, a nationwide organization that works to prevent and solve crimes, has offered a $10,000 reward for information leading to the culprit and two Missouri Congressmen have added $3,000 more.

St. Louis County Police Chief Jon Belmar said at a news conference on Thursday that muzzle flashes were detected from about 125 yards (375 feet) away from the rally.

The shooting came less than three months after a troubled man ambushed two New York City patrolmen, apparently seeking to avenge the killings of Brown and an unarmed black man in New York.

While you were sleeping, this also happened...