CINCINNATI – A white police officer whose fatal shooting of an unarmed black man led to three nights of rioting was careless and lied to police investigators to save his job, a prosecutor told a judge yesterday.

Prosecutor Stephen McIntosh said in closing arguments that Officer Stephen Roach had his finger on the trigger of his revolver and fired in a dark alley rather than use other means of stopping the fleeing suspect.

Other officers who had been chasing Timothy Thomas, 19, on April 7 testified they had not drawn their weapons or perceived a need to do so, McIntosh told Judge Ralph E. Winkler in Hamilton County Municipal Court.

“At some point, Officer Roach is moving down the alley with his finger on the trigger, discharging the weapon into the darkness,” McIntosh said. “Tim was essentially cornered. There was no place to go.”

Winkler, who heard the case without a jury, said he will announce his verdict tomorrow at 11 a.m.

The rioting in April was the city’s worst racial unrest since the Rev. Martin Luther King Jr.’s assassination in 1968. A citywide curfew was ordered, dozens of people were injured and more than 800 were arrested.

Roach, 27, is being tried on misdemeanor charges of negligent homicide and obstructing official business. If convicted of both charges, he could be sentenced to up to nine months in jail.

McIntosh said Roach told homicide investigators differing versions of what happened on the day of the shooting and three days later “to salvage his job.”

Defense lawyer Merlyn Shiverdecker said Roach was doing his job by trying to arrest a suspect fleeing arrest warrants. Thomas was wanted on 14 charges, including traffic offenses and fleeing from police to avoid arrest.

Investigators failed to take into account the lack of light in the alley and how involuntary fear reactions governed the officer’s response, Shiverdecker said.

Shiverdecker also pointed to expert testimony the defense presented on how dim conditions can affect perception and how the body’s involuntary fear reactions dictate an individual’s responses over reasoned choices.

The prosecution failed to counter the scientific testimony, and the state’s chief witness, police homicide investigator Charles Beaver, did not investigate those elements at the scene, he said.

“He was precipitous and premature,” Shiverdecker said of Beaver. “His logic was faulty and flawed.”

Roach declined comment in the courtroom after sitting quietly for the two-and-a-half hours of closing arguments.

He did not testify in the trial. Shiverdecker, said he decided to rely on other witnesses to present his case.

A Cincinnati officer since 1997, Roach is working in the police lot for impounded vehicles and is receiving pay while the case is pending.

Roach initially told investigators that Thomas made a threatening move toward him, and he thought Thomas had a gun. Homicide investigators said there were discrepancies between their evidence and his April 7 statement, and they asked him to make a second statement.

Roach then said, on April 10, that Thomas stepped around a corner in the alley and startled him, and that the officer accidentally shot him.

Police later found that Thomas had no weapon.