On Jan. 1, 1984, my brother, then 18, went to a video arcade in our neighborhood on Manhattan’s Upper East Side. It was 6 in the evening and kids gathered outside. Inside, five people played the slot machines.

Two young men entered and started bullying people. My brother tried to leave. One of the men pummeled him in the stomach, and his friend came from behind with a baseball bat. When police arrived, my brother was nearly dead. Surgeons operated, but put his chances of survival at less than 10 percent. He died the next day.

Police found the strangers who killed him. One was convicted of manslaughter and served 7 years in prison. The one who wielded the bat pleaded guilty to manslaughter and was sentenced to up to 26 years in prison.

I kept tabs on the guy in prison. I went to several parole board meetings. The head of the New York City parole board said authorities would keep him in prison as long as they could.

The goal in my meetings with the parole board was simple: I wanted him to stay in jail. I didn’t want to hear from another family if he killed again.

I can now say that it will not happen. Richard Dinneny, the man who wielded the baseball bat, is dead. He walked out of prison a decade ago, after 21 years. A single shot to his chest ended his life in mid-July. He was 53.

advertisement | advertise on newsday

Dinneny, who lived in upstate Orange County, was killed by a cop. With all the attacks against police, there are too many stories that never get told. This cop was doing his job protecting society from a bad guy.

On July 14, Dinneny’s ex-girlfriend called cops in Middletown to report that he had arrived at her apartment with a gun. She had filed an order of protection against him.

Dinneny spoke to officers from her apartment and told them he had a gun and would shoot cops if they came to the door. He ignored repeated orders by police to drop the gun.

The officers were well aware of the threat.

Dinneny was intoxicated, according to news reports, and came outside and stood with his gun, threatening the officers. They asked him repeatedly to put down the gun. He did not. One of the officers raised his gun and shot him dead.

It turned out that the Dinneny was threatening them with a pellet gun.

I write this opinion piece because we live in very precarious times. I want police officers to know that he was a dangerous man. Years after he killed my brother, I learned that Dinneny the teenager was being treated for drug addiction at South Oaks Hospital in Amityville and told a therapist he had a fantasy of killing someone. He then walked out of the hospital without anyone knowing, according to police reports. Within days, there was a warrant for his arrest. Two months later, my brother was dead.

I want police officers to know that he amassed a juvenile record filled with violence. During Dinneny’s trial, Justice Jeffrey Atlas told my family that even this man’s kindergarten record presaged a person who was destined to kill. Sadly, it was my brother. If not him, it would have been someone else, the judge said.

advertisement | advertise on newsday

I imagine that Dinneny didn’t even remember the name of the person he killed. My brother — his name is Jonny Habib — would have just celebrated his 51st birthday.

I am relieved that Dinneny is dead. Not an-eye-for-an-eye kind of thing. I am just happy that the world is free of another predator. The police were doing their job. At personal risk, officers showed up at an apartment under attack by a guy with a gun.

They were protecting society. They were protecting me — and you.

Jamie Talan is a former science reporter for Newsday and assistant professor of science education at Hofstra Northwell School of Medicine.