TERRY BOWEN has waited more than a year to hear if authorities would bring criminal charges against an off-duty Philadelphia police sergeant who allegedly gunned down her unarmed son.

Unbeknown to Bowen, former District Attorney Lynne Abraham - in one of her last acts as top prosecutor - decided not to press charges against the cop, Chauncey Ellison.

"We received a letter of declination from the District Attorney's Office saying they're not going to prosecute. I think it came out on New Year's Eve," Police Commissioner Charles H. Ramsey told the Daily News last night.

No one bothered to tell Bowen, whose son Lawrence Allen died last February, three months after Ellison allegedly shot him in the back during a bizarre dispute in West Oak Lane. Allen, 20, was left paralyzed from the chest down. He dropped more than half his body weight and battled numerous infections before dying, his mother said.

"I am so furious," Bowen said, after a reporter informed her of Abraham's decision. "No one ever got in contact with me."

Bowen said she was further incensed to see quick action taken in a similar incident involving an off-duty cop who shot an unarmed man, while the officer accused of shooting her son has remained on the force.

Officer Frank Tepper was given his walking papers on Monday, less than two months after he fatally shot William "Billy" Panas Jr. during a fracas in Port Richmond that involved Tepper's relatives. A grand jury is reviewing evidence in that case.

Ramsey said Allen's family "will just have to be patient. We have not forgotten about the case."

The commissioner said he was reviewing the police Internal Affairs investigation into the shooting and plans to decide "within the next two weeks" if Ellison should face discipline for any departmental violations in the shooting.

District Attorney Seth Williams also plans to "review the case thoroughly," and could ultimately press charges against Ellison, even in light of Abraham's actions, said Williams' spokeswoman, Tasha Jamerson.

"The case hasn't been dismissed," Jamerson said, noting that she couldn't comment on the letter that Abraham sent Ramsey.

At a news conference earlier in the day, Williams said one of his goals is to expedite investigations into police-involved shootings, "so that those officers who should be exonerated are exonerated, and those that should be charged are charged."

Neither Abraham nor her former spokeswoman could be reached for comment last night.

Witness accounts of the Nov. 17, 2008, incident painted Ellison as an angry father who was trying to exact revenge that night on a group of young men who he believed had assaulted and robbed his 14-year-old son.

Police said that Ellison's son was slugged and robbed of his pizza outside Bruno's Pizza, at 19th Street and Cheltenham Avenue, about 9 that night.

The boy explained the incident to his father, a nine-year veteran of the force who was off duty at the time.

Ellison confronted the suspected assailant, 17-year-old Demetrius Haywood, who darted up Renovo Street near 20th with the stolen pizza in hand.

Witnesses said that Ellison drove his SUV the wrong way up Renovo Street, then jumped from his SUV, pulled his police-issued firearm and identified himself as a cop to a group of people, including Allen, who was outside his home on the block. Ellison exchanged words with Allen, who contended that he hadn't been involved in the robbery.

Ellison was accompanied by another off-duty officer, Robin Fortune, who loudly encouraged him to stand up to Allen, witnesses said. Allen turned to go inside his house, "and that's when he [Ellison] shot him in the back," Bowen said.

Ellison fled the scene, but returned later when police arrived and said he believed that Allen was reaching for a gun. No weapon was ever found. Ellison has been on desk duty since the incident.

Allen, a father of three, never made it home again. He spent the rest of his life in a hospital, battling pneumonia and other infections, fallout from a bullet that punctured his lung and fractured his spine in nine places, his mother said.

"When he died, he was 60 pounds," Bowen said. "He suffered the whole time."

Allen's family filed a civil lawsuit against the city in May. "I want to see something done to this cop," Bowen said. "Be fair. If you're going to fire [Tepper], fire him too."