Leonard Lee, a lifelong Dorchester resident and antiviolence crusader, had just sat down for dinner Monday after a long day at work when he heard someone shouting outside his window: “Put the gun down!’’

Lee rushed to the window — on the second floor of the home he has lived in for 20 years — and looked outside toward the street, he said, where a deadly confrontation between a 19-year-old Boston man and two city police officers was unfolding.

The front of the home faces Penhallow Street, where the officers had arrived on bikes after a chase shortly before 5:30 p.m. Lee said there were no trees obstructing his view, so he could see the teenager clearly — down to the horror in his eyes.

“Put the gun down, put the gun down,’’ the officers screamed several times, Lee said.

As someone who has devoted decades to working with at-risk youth, Lee has seen the effects of violence on the front and back ends of urban confrontations. He’s never watched the whole thing play out before his eyes.

Lee said he saw the teenager, later identified by police as Jaymil Ellerbe, holding a handgun and backing away from the officers. The police had arrived on Penhallow Street after responding to reports of shots fired in Town Field in Fields Corner. They had seen the teenager and a second suspect running from the park onto Melville Avenue and were now in a face-off.

Lee, who did not know Ellerbe, said he saw the officers get off their bikes and implore the teenager to put the gun down.

Lee said he also began screaming: “They are going to kill you. Put the gun down. Put the [expletive] gun down.’’

The teenager looked up at him, Lee said.

“He could have easily shot me because I was in clear view,’’ said Lee, who kept looking out his window.

Lee said he saw the teen fire two shots in the direction of the officers, who ducked for cover behind Lee’s brown Volvo, which was parked on the street.

Lee said Ellerbe continued to walk backward down the street while facing the officers.

Everything went in slow motion, and Lee felt frozen in the window, fearing the worst.

“I wasn’t thinking of moving,’’ Lee said. “I responded. It wasn’t until later that I said, ‘What the hell am I doing?’ ’’

Ellerbe stopped at a small tree and took two more shots at the police, and that was when, Lee said, the officers returned fire.

One of the shots appeared to hit Ellerbe in the left leg. He fell, Lee said, but kept holding the gun, which was pointed to the sky.

The officers, along with Lee, repeated their plea: Drop the gun.

“I was screaming . . . as loud as I can because I [thought] that if he didn’t put the gun down they were going to continue to fire at him,’’ Lee said.

But, Lee said, he saw the teenager point the weapon at the officers. Then there were gunshots.

Lee said he saw the teenager jerk as though he had been hit in the stomach and then in the left shoulder. Then he was still.

Lee said he saw one of the officers run toward Ellerbe.

The other officer shouted, “He’s still alive. Don’t go over there,’’ Lee said.

The first officer continued to approach Ellerbe and then knocked away the gun, and immediately performed cardiopulmonary resuscitation, Lee said.

“Come on. Hang in there,’’ the officer said, according to Lee.

Then Lee heard him say, “He’s deceased.’’

At that time, Lee said, he bolted downstairs and outside.

“And I just started bawling. I lost it. This kid . . .’’ he said, choking up and pausing. “I could see the white in his eyes and he was distraught. He just lookedlike my son. He looked like my nephew. He looked like the kids I worked with over the years.’’

Lee said the teenager did not look like he was “trying to shoot his way out of this.’’

And, he said, the officers showed a lot of restraint in trying to end the confrontation peacefully.

Lee has headed nonprofits and was part of the “Boston Miracle’’ in the 1980s that helped curb gang crime. He also ran the Division of Violence and Injury Prevention for the Department of Public Health.

In short, he’s seen a lot of the effects of violence through the years. But this was something else, something more profound.

“I don’t know why God put this experience in front of me,’’ he said.

He wished he could have done more to save Ellerbe. It haunts him.

“I took responsibility I should have been able to save this kid’s life,’’ he said. “I know the cops . . . based on their temperament and how this went down, I know they didn’t want to kill this kid.’’

Meghan Irons can be reached at meghan.irons@globe.com.