UNION -- An off-duty Newark officer fatally shot a Piscataway man outside a popular Union pub in the early morning hours on Friday, acting Union County Prosecutor Grace H. Park announced Friday.

The shooting occurred after an altercation between the two men and is under investigation, Park said.

The shooting took place outside Paddy's Place on the 900 block of Rosemont Avenue.

The victim was identified as Michael Gaffney, 37, of Piscataway. Park did not release the name of the officer.

Park said Union Township officers responded to the scene and found the body of Gaffney around 1 a.m. He was pronounced dead at the scene.

The preliminary investigation -- which involves the Prosecutor's Office's Homicide Task Force and Special Prosecutions Unit, the Union County Sheriff's Office Crime Scene Unit, the Union County Police Department Ballistics Unit, and the Union Township Police Department -- determined the officer used his service weapon after the altercation, Park said. The officer was taken to an area hospital with non-life-threatening injuries, she said.

"It is our belief the entire incident is captured on video and when the investigation is completed it will show he was justified in his actions," Newark Fraternal Order of Police President James Stewart Jr. said of the officer.

Newark Public Safety Director Anthony Ambrose said the officer is an 11-year veteran of the city's police division.

"We will not comprise his safety by revealing his name," Ambrose said in a statement.

Park said the investigation remains ongoing and is being conducted "in strict accordance" with the New Jersey Office of the Attorney General guidelines governing all investigations into incidents involving use of deadly force by law enforcement.

Anyone with information about this matter is being urged to contact Prosecutor's Office Detective Kalebota at 908-527-4567.

Jessica Remo may be reached at jremo@njadvancemedia.com. Follow her on Twitter @JessicaRemoNJ. Find NJ.com on Facebook.