Inciting the ire of black leaders, a Cincinnati grand jury handed down two misdemeanor charges Monday against a white police officer whose fatal shooting of an unarmed black man touched off three nights of devastating riots last month.

As the sun set over the city, there were scattered reports of broken windows around downtown, where many businesses had been boarded up in case of new violence. About 150 people marched peacefully at police headquarters chanting "No justice, no peace" as officers on horseback and in riot gear watched nearby in a steady rain. The protest dispersed after an hour.

Officer Stephen Roach was charged with negligent homicide and obstruction of official business exactly one month after 19-year-old Timothy Thomas was shot as he fled down an alley.

Thomas' mother, Angela Leisure, was quick to criticize the grand jury's choice of misdemeanor charges for the incident.

"I feel it was a slap on the wrist," she said. "I don't feel like justice was served. I feel it was not severe enough for the severity of what he did. He took a life. Negligence -- that doesn't cut it for me."

She added: "My feelings are borderline rage."

Roach, 27, has said he thought Thomas was reaching for a gun and his attorney said he planned to enter innocent pleas. If convicted of both charges, Roach would face no more than nine months in jail and could receive probation.

"I know that emotions are running high over the tragic death of Timothy Thomas, but the case against Officer Roach cannot be decided based on emotion," prosecutor Michael Allen said.

Thomas, being sought for 14 outstanding warrants, was the fifth black man killed in confrontations with Cincinnati police since November and the 15th since 1995.

The shooting prompted the city's worst racial violence since the 1968 assassination of Martin Luther King Jr. in Memphis, Tenn. Dozens were injured during last month's unrest and more than 800 arrests were made before a citywide curfew helped restore order.

Prosecutors announced the grand jury's decision after most downtown workers had gone home. The Cincinnati Reds, who play downtown in Cinergy Field, are out of town until Friday.

The Rev. Damon Lynch, one of the city's most prominent black leaders, called for peace but criticized the grand jury's decision.

"I was expecting exactly what we got -- or less," Lynch said.

The Rev. Jesse Jackson and Kweisi Mfume, president of the National Association for the Advancement of Colored People, both said they were disappointed by the indictment. Jackson said: "Killing an unarmed person is not a misdemeanor, and to say so is to cheapen the life of a black person."

Earlier Monday, the Justice Department said it has formally opened a civil rights investigation of the Cincinnati police department. An agency official speaking on condition of anonymity said authorities would look for patterns of illegal conduct, including the use of excessive force.

Fifteen blacks and no whites have died in confrontations with Cincinnati police in the past six years. Authorities said most of the suspects pointed guns or shot at officers.

Two white officers are awaiting trial in one of the deaths. The coroner said Roger Owensby Jr., 29, suffocated during his Nov. 7 arrest.

Roach is accused of negligently causing Thomas' death and with giving misleading statements to investigators.

Allen said grand jury witnesses indicated that Thomas was wearing oversize pants and fled with his hands at his waist. He refused to elaborate on how the officer could be considered negligent.

Roach, a police officer since 1997, had been on paid leave but the department announced Monday night that he would be returned to desk duty.

Roach's lawyer, Merlyn Shiverdecker, said his client would plead innocent.

"Nobody's happy being indicted," Shiverdecker said of his client's reaction. "It's my expectation that the case will proceed to trial."

Mfume, who spoke with Thomas' family Monday, described the situation in Cincinnati as "very tense."

"I have oftentimes described it as ground zero for race relations in our nation," Mfume said from his office in Baltimore, Md.

Blacks have long complained they are harassed by Cincinnati police and their neighborhoods are neglected economically. The American Civil Liberties Union and black activists sued the city in March, accusing the police department of failing to end 30 years of police harassment of blacks, who make up 43 percent of the 331,000 residents.

In the past month, the City Council has agreed to federal court-supervised mediation to resolve the ACLU lawsuit and the city's safety director and the city manager have resigned under criticism.

Mayor Charles Luken has also established a commission on race relations to explore problems that led to the rioting and what should be done to improve housing, employment and education for blacks who say they have been left out of Cincinnati's economic growth.

The Associated Press contributed to this report