It was about 8:30 on a chilly December morning when the body hit the floor. Nobody said a thing; a man face-down on the gray tiles of the Civic Center BART station is not an uncommon sight. People kept moving. He stayed still.

But there was one person who stopped. Sometimes it only takes one.

The commuter mistook Frank Altamirano for a cop and flagged him down. Altamirano is not a cop. He’s an elevator attendant. But that wasn’t important. What was important was that, when the commuter asked Altamirano if he had any Narcan, the answer was “yes.”

Altamirano saw the needle next to the prone man’s bag. He checked for a pulse. There wasn’t one: “He was starting to change colors,” he said.

Altamirano, 56, is a burly Mission native with broad shoulders and a linebacker’s build; he flipped over the dying man and plunged the opioid-reversal spray into his nose. “You could literally see his heart start beating again,” he said.

Paramedics bundled the overdose victim off to the hospital. Altamirano stood to the side and watched him go. Saving a man’s life is a profound experience. For anyone. But for Altamirano, it goes deeper than that. Very few of us can demark the point in time when our lives come full circle. Altamirano can.

“I had to have compassion for this man,” he explains, “because of the damage I have done.”

“In all actuality,” Altamirano tells me, “I should have stayed there. I should have at least tried to revive him. Call an ambulance. But I cared more about myself. So I took off.”

We’re tucked away in the corner of the Civic Center station on an easy-to-miss wooden bench, not far from the restrooms that no member of the public has had the pleasure of using since Sept. 11, 2001.

Altamirano missed 9-11. He missed three 49ers Super Bowls and three Giants World Series and relatives being born and dying and everything in-between.

We’re not talking about the December 2018 morning he made a man’s heart start beating again. We’re talking about the November 1985 night when he did the opposite.

By the time he got back to his home on Valencia Street, the cops were already there. They knew who he was, they knew where he lived — and they knew what he did.

“The moment I put my key in the door, they had guns drawn on me,” he recalls. “And my mother was looking through the window. The last thing she saw was people pointing guns at me and putting me into the police car. I had to apologize to her for that.”

There have been many apologies. “I ruined two families that day.”

An easier question to answer than what drugs Altamirano was on that night might be: what drugs wasn’t he on? They were drinking. They were smoking weed. There was some PCP. Maybe a little cocaine, too. And, after all that, his Mission crew meandered its way down to Marina Green. This was a normal place to end up, after you’d done all of the above, to meet up with your neighborhood pals. And continue doing all of the above.

“You knew the faces. Especially everyone who grew up in the Mission, you’d come down there to cruise. So you knew the people from the Excelsior. Daly City. Crocker Amazon.” And, on this night, South City. Out-of-towners were not warmly welcomed. Words were exchanged. And then more. When Altamirano approached a car full of South City folk, he says he thought a man named Abel Valle was reaching for a weapon.

He wasn’t. But Altamirano did. He slashed at Valle with a knife, and stabbed him in the heart, killing him. Valle was only 20 years old. His daughter was an infant. Valle would never see her grow up.

But Altamirano would. Through the years, there she was, in the front row of his parole hearings.

Frank Altamirano was paroled in 2017. He never expected to be. “I was already planning my own funeral,” he admits. “After 30 years, you give up hope.”

Nowadays, Frank Altamirano’s alarm clock goes off every day at 3 a.m. But, truth be told, he’s almost always already up. He lives in a below-market-rate unit only a hop, skip, and a jump from Civic Center BART, and he’s there at 4 a.m. to unlock the gate for the early-morning crew of elevator attendants he supervises.

Like The Fonz, Altamirano’s office is in a restroom. He goes through paperwork here, and makes sure his colleagues’ radios are charged. If a co-worker needs to use the toilet, he can do paperwork outside.

Altamirano works for Hunters Point Family, the nonprofit that mans the BART elevators at Civic Center and Powell stations as well as the Pit Stop toilets at 24 locations throughout the city. These programs, in fact, work in concert with one another. Instead of using BART elevators as a toilet, now desperate people can be directed to a nearby Pit Stop.

Until Altamirano and others inaugurated the attendant program at Powell and Civic Center in May, BART had no idea how many people used its elevators. The statistics the attendants keep are insanely detailed: They denote adults, children, service animals, pets, luggage — and, of course, “feces/urine” and “needles.”

Those last two have dropped to zero since May. With an attendant in all four elevators every minute they’re running, nobody is intentionally stalling them to shoot up, take a whiz, or anything else. Lena Miller, the executive director of development at Hunters Point Family, notes that disabled people — who had been forced to roll their wheelchairs through human filth in order to use those elevators — wept with joy at the onset of this program. Some of them had been assaulted between floors. Others had been stuck with stray needles.

Altamirano and his colleagues have created a more dignified experience for the men and women who need these elevators, and opened their doors to a broader group of users who merely want them (the number of people bringing luggage into the elevators has roughly quintupled since May).

And, at the same time, doors have been opened for the attendants, too.

Growing up in the Mission, Altamirano was a Norteño. But, he says with a wan smile, he had to go to prison to learn what being in a gang was all about. Inside, “it was a strict regimen. Like the military. Sleeping in shifts. Waking up at 3:30.” Synchronized calisthenics in the yard like a kung-fu army in a Bruce Lee movie. Moving dope within the prison walls. Moving smartphones for $1,000 a pop or burner phones for $500 (“even Charles Manson had a phone” in prison, Altamirano notes).

All of this required decades of emotional detachment. “I just shut myself off,” he says. “What I learned about my prison experience is, if I’ve known you 15 or 20 years, and I need to hurt you, I can’t have any feelings about it. Don’t take it personal. That’s just the way it is in here.”

But that’s not how it is out here. When Altamirano sees his “former rivals” in San Francisco, they shake hands. They exchange information on how to get help and resources. They treat each other like people.

Frank Altamirano gets up at 3 a.m. and works a taxing and mentally challenging job, underground. But he considers himself to be fantastically lucky. Because he can feel again. He can be fully human.

Is spending long hours in an elevator uncomfortable for a man who’s been incarcerated most of his life? Altamirano offers a patient grin. He’s asked this question a lot.

The answer is complicated. The truth is, Frank Altamirano’s cell is his own mind. At night, his dreams are always about being incarcerated again. He never dreams about being free. That makes it hard to sleep. That makes it easy to get up at 3 — or before 3 most days — and start working.

In his mind, he continues to cope with the issues that led him to substance abuse, violence, and doing things he could not undo. That will never end. That’s a life sentence.

But, now, he can do more than think. He can do. He can help people. He can even save people.

In the elevator, the door will always open. And you can walk right through.

And then, you’re free.