A federal jury convicted a Prince George's County police officer yesterday of violating the civil rights of an unarmed homeless man by releasing her police dog to attack him even though he had surrendered.

The jury in U.S. District Court in Greenbelt deliberated more than nine hours before finding Officer Stephanie C. Mohr guilty of violation of civil rights under color of law, a felony. The same jury acquitted county police Sgt. Anthony Delozier of conspiracy. Both were being retried after a jury deadlocked on those charges in March.

The conviction of Mohr, 30, is a rare victory for federal prosecutors as the Justice Department pursues a comprehensive probe of alleged brutality and discrimination in the Prince George's Police Department and the FBI conducts more than 30 criminal civil rights cases stemming from such incidents.

Mohr is believed to be the first county officer to be found guilty at trial of a federal civil rights violation, and her conviction comes after prosecutors persuaded Judge Deborah K. Chasanow to allow testimony about earlier attacks and incidents in which Mohr was involved.

The jury in Mohr and Delozier's first trial was split 11 to 1 in favor of acquittal, and several jurors said in interviews that they were not convinced Mohr had acted improperly in the September 1995 attack.

Ralph Boyd, assistant attorney general for civil rights whose office spearheaded the prosecution, said yesterday that "when police officers cross the line and abuse their authority, as this verdict shows, we will vigorously prosecute them to protect the fundamental rights of all persons in the United States."

Prince George's Police Chief John S. Farrell was at the courthouse after the verdict and said that the department would move quickly to fire Mohr. He said Delozier would remain on paid suspension pending an internal investigation into whether the sergeant violated departmental rules in connection with the dog bite attack and the investigation into it. Delozier was accused of asking permission to allow Mohr to release her dog.

Farrell said of the Mohr conviction: "I don't feel this verdict reflects the actions of the majority of Prince George's County police officers. I think it's a tragedy for all concerned."

Police spokesman Royce D. Holloway said police investigators would also review the trial transcript for possible wrongdoing by other officers, including James Santos. Santos is named in court records as an unindicted co-conspirator. Federal prosecutors allege that Santos beat a second homeless man while Mohr's dog bit the first one.

Questions about Mohr's activities and those of other Prince George's canine unit officers have been raised repeatedly in recent years in civil lawsuits brought by people attacked by police dogs and in an April 1999 Washington Post story chronicling those incidents.

Two recent Post series also detailed the tactics homicide detectives used to obtain false confessions from four men, who were later exonerated, and showed that over 11 years, county officers had shot and killed more people, per officer, than any other large police department in the nation.

The jury forewoman announced the verdicts, in a barely audible voice, about 4 p.m. before a courtroom filled with relatives and supporters of Mohr and Delozier, reporters and courthouse workers.

Mohr appeared shocked and began weeping as her attorney, David M. Simpson, tried to console her. She left the courthouse by a rear exit.

"The verdict was a surprise," Simpson said. "Obviously, she's distraught. She's extremely disappointed. Shock is probably the best way to describe it."

Delozier also appeared shocked by the verdict regarding Mohr. "It wasn't right. She shouldn't have been found guilty," Delozier said.

Mohr faces a maximum sentence of 10 years in federal prison and a fine of $250,000, though her sentence is expected to be less than that under federal sentencing guidelines.

Chasanow scheduled sentencing for Nov. 19 and allowed Mohr to remain free until then.

The retrial of Mohr and Delozier focused on a Sept. 21, 1995, incident behind a printing shop in Takoma Park.

Takoma Park police conducting a burglary stakeout spotted two men, Ricardo G. Mendez and Jorge Herrera-Cruz, on the roof, and county police canine unit officers and a state police helicopter were called in for backup.

According to court testimony, Mendez and Herrera-Cruz complied with police commands to come down from the roof and put their hands in the air. Mendez, a Mexican national, and Herrera-Cruz, a Salvadoran, both testified that they turned and put their hands on a wall as several police officers pointed their guns at them. Police quickly learned that Mendez and Herrera-Cruz were not burglary suspects but had been sleeping on the roof.

Prosecutors said that with Delozier's permission, Mohr released her police dog on Mendez and that the animal bit a chunk out of the man's leg.

In the retrial, Assistant U.S. Attorney Steven M. Dettelbach and Alexander H. Busansky presented a tighter case against Mohr and Delozier, with more police witnesses who testified that the two men never ran or presented a threat.

A key government witness was Dennis W. Bonn, a retired Takoma Park police sergeant who testified that he gave Delozier permission to have Mohr release her dog. Bonn, who pleaded guilty to accessory after the fact in the case, said Mendez and Herrera-Cruz never tried to run or resist.

Prosecutors also presented evidence they said showed that Mohr had a history of using her police dog to brutalize and terrorize minorities.

A teenager testified for the government that in 1997, Mohr, who was tracking a burglary suspect, released her police dog to attack him while he slept in a hammock. A woman testified that Mohr threatened to set her dog on the woman's "black ass" while officers searched her home for her brother, a parole violator. The teenager and the woman are black; Mohr is white.

Despite the raft of brutality lawsuits against her, Mohr was never disciplined by the police department for any of the incidents, though she was fined $100 for making a false statement during an internal investigation into a training mishap in which another officer was mistakenly bitten by her dog.

According to a police department memo that surfaced in court records, not a single report of excessive force by county police canine unit officers has been sustained by police in the last decade.

After yesterday's verdict, Dettelbach said: "Police are accountable to the citizens for their actions. That's the system we have."

Staff writer Dan Eggen contributed to this report.

Prince George's County Police Officer Stephanie C. Mohr arrives at the courthouse before being convicted in the dog attack.Sgt. Anthony Delozier leaves the federal courthouse in Greenbelt after being acquitted of instructing another officer to release her police dog on an unarmed homeless man in 1995.Sgt. Anthony Delozier, left, and attorney William C. Brennan leave the courthouse. "She shouldn't have been found guilty," Delozier said of fellow officer Stephanie Mohr.