When they reached out to try to grab hold of the man, Rocha said, “He just went for his knife.” The officers went for their guns, and Rocha went for his camera.

“When I saw the officers draw their guns, I was sure they would kill him,” the Brazilian tourist said Sunday, the day after the man, 51-year-old Darrius Kennedy, was shot to death by police, who said he had lunged at officers with the 11-inch (28-centimeter) kitchen knife.

“If they’re going to kill him, I want to take some pictures, I want to record it,” Rocha said.

Kennedy was smoking marijuana near the military recruiting station in Times Square about 3 p.m. Saturday when officers first approached, police said. It was the beginning of an encounter that would stretch for seven of the most crowded blocks in New York City in midafternoon and end a few minutes later with 12 gunshots and many witnesses.

As officers spoke to Kennedy, he became agitated, pulled out the knife and began to put a bandanna on his head, police said. He ignored repeated orders to drop the knife and began backing away from them, continuing for blocks as he waved the knife and drew many officers into a slow-speed pursuit that itself lured onlookers.

Rocha said the unusual scene was the first time he had ever seen anything like it in any of his several visits to New York City.

“You see something like this, you want to record it,” he said. And in Times Square, crowded with countless tourists, street vendors and New Yorkers, many others apparently felt the same way.

Though Rocha stayed put, held back by his wife’s insistence, the others following the chase pulled out cellphones to capture footage and, in some cases, offer commentary.

“They’re going to shoot you, boy,” a man’s voice is heard yelling on a video that an onlooker provided to The New York Times.

Numerous officers can be seen going down the street in another video on the website of the New York Daily News.

According to the police, officers pepper-sprayed Kennedy six times but he held onto the knife throughout, wiping the spray off his face. Finally, he lunged at police and two officers shot him in the torso, police said.

In one video segment, police cars with sirens blaring pull up as gunshots are heard. Officers moved quickly to corral onlookers.

Kennedy was pronounced dead at Bellevue Hospital.

Rocha acknowledged that it made a difference that Kennedy was only holding a knife, and that there were so many officers on scene.

“If it was a gun, a revolver, I don’t know that people would stay there and take pictures,” he said.

“I just stayed because I saw he was holding a knife,” Rocha said. “I was behind the officers, I knew he couldn’t reach me.”

Kennedy, who lived in Hempstead, New York, and was a native of South Carolina, had been arrested 10 times, including seven for marijuana possession, police said. In 2008, he was taken to a hospital for observation after knocking down garbage cans in Times Square.