‘It was my calling to be here with you today.’ When a police officer got shot, this ex-con had a choice to make.

(CNN) — John Lally was on his third gravel delivery of the day Saturday morning when he saw flashing police lights in the rearview mirror of his pickup truck and immediately thought he was being pulled over.

Lally, who’d had his own serious run-ins with law enforcement over the years, slowly pulled off to the shoulder of US Highway 59.

But it wasn’t Lally police were after.

Officers had identified a stolen car and tried to make a traffic stop. But their 19-year-old suspect, unrelenting, took off – fast – on a busy Houston artery.

Then, “out of nowhere … it sounded like an explosion,” Lally told CNN. “I saw a car flip over. I saw a tire in the air.”

The suspect had crashed into other cars – six or seven, Lally said – disabling the stolen car and stopping traffic across the main lanes of the freeway, police later said.

After seeing it all unfold from his truck, Lally thought he’d seen it all.

The delivery driver was only five minutes from his destination, he said. But he knew, with traffic blocked, he wouldn’t get there on time.

So, to prove to his boss why he’d be late, he started recording the aftermath of the crash on his cell phone – and got out of his truck.

Also stepping out of his vehicle at the collision site was Houston Police Officer Jonathan Gibson. He shouted commands to the suspect, police said.

But the teenager didn’t listen.

Instead, the suspect fired a gun, police said.

Lally heard shots, he recalled, and knew this had turned into more than a police chase.

He crept around his truck, making his way toward the back. That’s when he saw it:

Gibson – who never fired his own gun – took a bullet to the leg, police said.

Lally – who’d once been shot in his leg – knew exactly what Gibson was enduring in that moment, he said.

And though he’d often found himself on the opposite side of an encounter with police, the delivery driver knew he had to act.

“In my mind,” Lally said, “I just was on a mission to go grab him.”

The suspect wasn’t subdued. Still, Lally headed toward the wounded 29-year-old officer.

“When I got to him, I just snatched him up by his vest, and me and another cop just dragged him to the back of my truck.”

The whole time, Lally’s cell phone kept recording.

“You’re OK, bro. You’re OK,” Lally told Gibson, the footage shows.

“Breathe.”

‘I’m still here with you, buddy’

“I’ve been to prison twice, man. I’ve been to state jail once. The last time I was locked up, they offered me 25 years, man. I had no choice but to get out and change my life. ..”

As more police patrols arrived, the suspect left the stolen car and tried to get inside another vehicle, police said.

Lally just kept trying to calm Gibson, his cell video shows.

Another officer ordered the suspect to put down his gun, according to police and the video.

But, again, the suspect didn’t listen.

Blocking all that out, Lally reassured Gibson – the dad of a 20-month-old, he learned – he had no intention of leaving his side.

“Hold my hand. You’re going to be OK. Hold my hand,” Lally assured Gibson again and again over almost 10 minutes.

Gibson winced and grunted as Lally kept talking, the cell phone video shows.

“I’m still here with you buddy, you hear me?” Lally reminded the officer several times.

“I know it hurts, man. You just keep squeezing my arm.”

Then, Lally got personal.

“I’ve been to prison twice, man,” the delivery driver said. “I’ve been to state jail once. The last time I was locked up, they offered me 25 years, man.

“I had no choice but to get out and change my life … and I’m here with you, like it was my calling to be here with you today.”

As the suspect exited a second car, officers fired their weapons at him, police said. He ran to yet another car but appeared to be hurt and fell to the ground.

Still ignoring the officers’ commands, the suspect loaded another magazine into his firearm, according to police.

Officers fired at him again – this time striking him more than once, police said. He was taken to a hospital and pronounced dead.

Gibson, police said, also was also rushed to a hospital.

‘I just know that he’s shot’

The officer, his department said, was in stable condition Monday and expected to make a full recovery.

By Tuesday, Houston Police spokeswoman Jodi Silva told CNN, he was headed home.

The shooting was under investigation by the Houston Police Department’s Special Investigations Unit, the Internal Affairs Division and the Harris County District Attorney’s Office, the department said.

The actions taken by Lally, meanwhile, deserve celebration, Houston’s police chief declared at a news conference while also acknowledging the alleged crimes and convictions in his past.

“People make mistakes,” Troy Finner said of Lally. “But a truly reformed individual is a person that we can use. And he stepped up and other citizens stepped up, and I don’t want that to get lost.”

Lally, for his part, never thought twice, he said: “It has nothing to do with them being a cop. I don’t have to like you … I just know that he’s shot and he’s going through it.”

In the end, the delivery driver said, he was just “at the right place and the right time.”

CNN’s Amy Simonson and Caroll Alvarado contributed to this story.