Before Bob Jackson snapped one of the 20th century’s most iconic news photos, the Dallas Times Herald photographer thought he had blown the chance of his career.

Two days before Jackson photographed Lee Harvey Oswald being shot to death in the basement garage of the Dallas police station — an image that would earn him the Pulitzer Prize and international recognition — Jackson missed documenting one of the most important events in U.S. history.

And he was depressed.

On Nov. 22, 1963, Jackson, a 29-year-old staff photographer for Dallas’ evening newspaper, was assigned to cover President John F. Kennedy’s arrival at Love Field and his motorcade through the city.

Jackson sat atop the back seat of a convertible, six cars behind Kennedy’s, as the motorcade approached Dealey Plaza.

His camera had no film.

Jackson, who now lives in Manitou Springs, had just tossed an envelope containing film to a reporter who was waiting alongside the motorcade route. They were laughing because a gust of wind blew the envelope onto the street.

“That’s when we heard the first shot,” Jackson said. “Then we heard two other shots closer together. I just looked straight up ahead of me at where the sound came from. On the fifth floor of the book depository, there were two men hanging out of the window and looking above them. That made me look up there too, and there was a rifle resting on the edge. Immediately, he drew it in.”

Jackson was among the few people to see the rifle in the sixth-floor window of the Texas School Book Depository. But the camera he was holding had no film.

But Jackson, 79, who spent a career as a photojournalist for newspapers in Texas and Colorado, including The Denver Post, has never tired of talking about the photo he did get — the famous one of Oswald — as well as the events leading up to that moment.

Still perched on the back of the car, Jackson watched bedlam unfold that Friday at the intersection of Elm and Houston streets. The president’s limousine sped away. A motorcycle cop jumped off his moving bike. A mother and father threw themselves over their children on the legendary grassy knoll.

Jackson stayed in the car while other journalists jumped out.

“As we went under the underpass, I could see the people’s faces,” he said. “I thought, ‘This is really bad.’ I decided to get out.”

As he ran on the street, he heard from witnesses that the president had been shot.

“I realized I screwed up,” he said. “I should have stayed in the car and headed to the hospital.”

He never did take a photo while at the plaza — another mistake.

“I should have started shooting people’s faces,” he said. “I thought, ‘I should get to the hospital. I have blown my assignment here.’ “

Jackson made it to the hospital but was kept at bay along with a growing throng of reporters and photographers. None had photos of Kennedy arriving at the hospital.

On the police scanner, Jackson heard that an officer had been shot and later that authorities had arrested a suspect.

“I went to the police station and stayed there with the mob of press throughout the night,” he said. He got some of the first photos of Oswald being led down the hall. He later shot a gripping photo of Oswald’s wife and mother in an elevator.

Sunday morning, Jackson was told to go to the police station and photograph the transfer of Oswald to the county jail.

Police were on guard because of death threats against Oswald. An armored car was set up to take the suspect from the police station. Delays dragged out the morning, and Jackson’s editors wanted to redeploy him and the reporter.

Texas Gov. John Connally’s wife, Nellie, was scheduled to make a statement at a news conference. Her husband, who had been seated in front of Kennedy, also was struck by a bullet. The city desk told Jackson and the reporter to abort covering the Oswald transfer and to head to the news conference.

“I couldn’t believe it,” Jackson said.

He told the reporter to tell the editor he was going to stay at the police station.

“This was another chance for me to get another picture of the man who killed the president,” he said. “It didn’t make much sense to leave the situation where your competition is standing next to you.”

Jack Beers, a photographer from The Dallas Morning News, positioned himself above the scrum.

Finally, officials told the gathered journalists that Oswald was coming.

“I picked a spot,” Jackson said. “I didn’t want to be too close to him. I had to make sure I wasn’t in the path of the cars. … I prefocused the camera about 11 feet in front of me.”

He made sure his camera was wound and his flash ready.

“They said, ‘Here he comes,’ ” Jackson said.

He peered into the viewfinder.

An unmarked police car began to back up. Oswald emerged from the elevator, handcuffed to homicide Detective Jim Leavelle.

“They were coming toward me,” Jackson said. “I had to make sure the car wouldn’t run over my foot. They stepped out. The car stopped. All of a sudden someone steps out, two quick steps.”

Jackson leaned over the fender, because a man was in his frame.

Later that day, the world would know that that man — Oswald’s killer — was Jack Ruby, a Dallas nightclub owner who told police he was hellbent on avenging the president’s death.

“He fired, and I hit the shutter,” Jackson said. “It just came together. Came together very nicely. I couldn’t have planned it better. … I was trying to get a photo before this guy blocked the view.”

Pandemonium ensued. A police officer grabbed the camera from Jackson, who told him to “get your hands off.”

When Jackson returned to the newsroom a couple of hours later, editors were already looking at Beers’ photo on the wire. It showed Ruby holding the gun in front of Oswald — but prior to firing it. The photo was a sensation. Newspapers around the world were picking it up. Jackson’s editors asked, “Do you have anything as good as this?”

Jackson headed into the darkroom.

“My big concern was did I get it before the bullet entered his body,” Jackson said. “I wasn’t so worried about it being sharp. I had direct flash. I was more worried about the timing.”

Jackson held up the wet negative to the light and was the first to see the image. “I realized that I had beat The News.”

Beers’ photo lacked the emotion, the drama. It foretold what was about to happen. It contained none of the horror and drama of Jackson’s image.

Jackson carried a wet print into the newsroom. “How does it feel to win the Pulitzer?” several people immediately asked Jackson.

It is now the famous black-and-white photo: Oswald, eyes shut and mouth in a tortured O; Leavelle in a tan suit leaning away from his contorting prisoner; and a hunched Ruby firing his pistol.

TV cameras and other photographers also captured moments of Ruby’s shooting.

No one produced an image like Jackson’s.

“If you look at the video, it is so disappointing compared to the still,” said Nina Berman, associate professor at Columbia University’s graduate school of journalism. “The still crystallizes this whole moment. You keep looking at it to see if anyone can see what is going to happen. … It is such a fantastically composed picture.”

Today, a print of the shot hangs above the TV in Jackson’s living room. In a safety deposit box in a Colorado Springs bank, the photographer keeps the original negative given to him by the publisher, Jim Chambers, who said, “I want Bob to make as much money off this picture as possible.”

Historians describe the events in Dallas that weekend as the country’s introduction to the effectiveness of live TV in covering news events. No one had ever seen a murder broadcast live before.

But Jackson’s photo has maintained the command that photojournalism always has and still does — the capability of telling a full story by freezing time.

“It’s one of those rare occasions where you have that sharp moment that you see the reaction, the impact and the instance of recognition,” said Keith Greenwood, assistant professor of photojournalism at the University of Missouri.

Jackson’s photo was taken a sixth of a second after Beers’. To this day, Jackson doesn’t believe it was luck. “I grew up Presbyterian,” he said, “and they always talked about predestination. I guess I was predestined to do it. It was just going to happen.”