Attorneys in Martinez Wednesday delivered closing arguments in the felony case of a former Richmond police officer accused of punching a handcuffed suspect during an arrest and trying to cover it up.

Prosecutors said that Dedrick Riley, now 42, used excessive force "under the color of authority and without legal necessity" the night of March 7, 2009, when he allegedly punched drug suspect Donald Stewart and filed a false report about the incident.

Both the suspect and Anthony Diaz -- the rookie police officer training under the defendant that night -- reported the incident, prompting an investigation and Riley's firing.

During closing arguments in Contra Costa County Superior Court Wednesday, Deputy District Attorney Barry Grove told the jury that Riley abused his power and hit the suspect out of anger, then lied to his superiors about it.

But Defense Attorney Harry Stern characterized Riley as a seasoned police veteran who was just doing his job that night, and painted Diaz as an inexperienced officer whose version of the incident is emotionally charged and unreliable.

He said there was no conclusive evidence to show Riley punched the suspect, and that the defendant reported what really occurred.

Diaz testified during the trial that on their shift that night, Riley pulled in front of Stewart's parked Acura near Third Street and Ohio Avenue and shone a spotlight into the vehicle, according to Grove.

Spotting cocaine inside the car, the defendant threw Stewart to the ground and handcuffed him, prosecutors said.

Grove said Riley was mad at the suspect for cursing at and taunting him and pulled a handcuffed Stewart up by his shirt collar, then slapped him and punched him twice in the head, Grove said.

"You can understand why he did it, but you can't condone it," he told the jury.

The attorney said Riley cut a deal with Stewart, letting him go as a confidential informant, and only two hours later casually mentioned to his superior that he had to "slap (Stewart) around" during the arrest to keep him in line.

Grove said that while the suspect's criminal history makes him a less credible witness, his version of the night's events closely matched Diaz' description of the incident to investigators.

"It's not a coincidence - it happened that way because it was exactly as Officer Diaz said it was," the prosecutor said.

In addition to not disclosing the force used in the arrest, there is also an "inherent inconsistency" in quickly releasing a suspect who was described during the trial as violent and high on drugs, Grove said.

He also reminded the jury of a previous incident where Riley allegedly used excessive force on a suspect, hitting his head against the hood of a car.

Court records show the defendant was fired from the Richmond Police Department a first time in 2006 after lying about his use of force on a homeless man who was causing a disturbance.

He later regained his job with back pay after filing a civil suit against the department.

On Wednesday, the defense focused on inconsistencies in the present case.

Stern told the jury that on the night of March 7, 2009, Riley only threw the suspect on the ground after he saw him trying to stomp on a rock of cocaine in his car -- a detail that Diaz corroborated.

He also maintained that apart from statements from Diaz and Stewart, who he said are unreliable, there is nothing to prove Riley punched the suspect, nor any evidence that Stewart did not resist arrest.

A neighbor who said he saw the incident testified that he only saw Riley slapping the suspect and that Diaz also subdued a struggling suspect, refuting Diaz' testimony that he "never touched" Stewart.

Stern said Stewart told officers shortly after the arrest that Riley had slapped him, but only mentioned being punched in later interviews.

The defense Wednesday showed jurors poster-sized photos of Stewart after the incident without any visible markings to suggest he'd just endured a beating.

"The absence of any markings completely casts doubt on those who say he got punched," Stern said.

Stern told the jury that unless they were able to cast off the reasonable doubt of Riley's guilt in the case, they could not convict him.

Jurors were set to start deliberations on Thursday.