An off-duty Trenton police officer's altercation with a man Saturday night ended with the man dead of a gunshot wound to the chest, New Jersey authorities said.

Officials with the Mercer County Prosecutor's Office said the incident unfolded about 9:50 p.m. on Roosevelt Street near West Ingham Avenue. Alfred Toe, 34, his brother Constantine Toe, 30, and the off-duty officer were attending a repast celebration following a funeral earlier in the day, according to witnesses.

"He was with us drinking," said James Alpha, Toe's friend. "Nobody knew he was an officer."

Officials say Alfred Toe got in a dispute with someone else at the party. He then allegedly went into his brother Constantine's car to grab a gun. That's when Constantine Toe confronted him and tried to wrestle the gun out of his hand, officials said. During the struggle, Constantine was shot in the hand but managed to get the gun away from his brother, according to investigators.

Witnesses say the off-duty officer then confronted Constantine Toe and took the gun away from him. He then pulled out his own service weapon and held Constantine Toe on the ground. Witnesses say that Alfred Toe, who did not know the man was a police officer, then jumped in and tried to grab the officer's gun. That's when the off-duty officer opened fire, according to the witnesses.

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"Next thing, pow! Everybody dropped!" Alpha said. "What's that for? How can I tell this man in sneakers is a regular police officer when you don't have your badge on? How can I tell?"

Alfred Toe was struck once in the chest. He was taken to the hospital where he later died from his injuries.

Friends of Toe told NBC10 they believe he would have acted differently if he had known the man was a police officer.

"Did you make it known to him that you were an officer? A peace officer in the city of Trenton?" asked George Weah. "You did not make it known to him. He sees you in civilian clothes on top of his brother. Mind frame? I have to get you off my brother. You have a gun at the back of my brother's head."

Officials have not identified the officer. Toe's friends are demanding a full investigation and want to know whether or not the officer was legally drunk during the incident.

"It's not only when a white cop shoots a black guy that everybody's eyes should be all over the place," said Michael Blidi, a friend of Toe's. "This is a black on black thing."

The Mercer County Prosecutor's Office is investigating the shooting.