Investigators are learning more about the gunman who killed a former co-worker outside the Empire State Building before being shot dead by police in a Friday morning confrontation that was caught on camera.

New York City police are trying to piece together what caused Jeffrey Johnson, a T-shirt designer, to ambush Steve Ercolino, an apparel company vice president, outside the Manhattan offices of the company where the two were once colleagues.

Details emerging in the aftermath of the attack paint the two men as opposites.

Johnson was a solitary birdwatcher who spent long hours in the quiet areas of Central Park, photographing hawks and marvelling over nature's beauty.

His victim was a gregarious salesman, beloved by his nieces and nephews as the fun uncle who could talk with equal expertise about the New York Jets and the women's fashion accessories he sold.

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In this sequence of images taken from a surveillance video camera, police officers approach Jeffrey Johnson after he shot his former colleague Steven Ercolino near the Empire State Building on Friday. (New York City Police Department/Associated Press)

Police said Johnson hid behind a car and then killed Ercolino with five gunshots as he arrived for work. Johnson was then shot by two police officers who confronted him on a busy sidewalk.

Security camera footage, which was released by the police, shows Johnson walking calmly down the sidewalk after the shooting, distancing himself slightly from the other pedestrians, who appear to have no awareness that anything is wrong.

But when two police officers approach in a hurry, Johnson turns and pulls a handgun from a bag, his arm cocked as if to fire. Then, the scene explodes into action.

The officers, who had no opportunity to take cover, fire almost immediately.

People seated on a bench behind the gunman and pedestrians standing close to the two officers run for their lives. Only a young child seems not to react, strolling out of view of the camera as adults all around leap away in terror.

2 officers fired 16 shots

The fatal encounter is over in eight seconds.

Authorities confirmed Saturday that all nine bystanders caught in the chaos were wounded by the two veteran patrolmen, who had never fired their weapons on duty.

Officer Craig Matthews fired seven times and Officer Robert Sinishtaj fired nine times. The wounded were likely struck by their stray or ricocheting police bullets, Police Commissioner Raymond Kelly confirmed Saturday. 

None of their injuries was life-threatening, police said.

Johnson legally bought the gun in Sarasota, Fla., in 1991, but he didn't have a permit to possess it in New York City, authorities said.

Gunman described as quiet loner

Police investigating Johnson's killing of Ercolino were eyeing bad blood between them from when they worked together at Hazan Import, a garment district business where Ercolino was a vice president of sales.

Johnson and Ercolino had traded harassment accusations when they worked together, police said, and when Johnson was laid off from the company a year ago he blamed Ercolino, saying he hadn't aggressively marketed his new T-shirt line.

After Johnson's layoff, neighbours said, he continued to leave his apartment every day in a suit.

Internet records listed Johnson as the administrator of the website for a business called St. Jolly's Art, which sold iron-on graphic art for T-shirts. Art for sale on the site included stylized drawings of fighter planes and muscle cars and whimsical "seafaring vignettes" featuring pirate maidens and tall ships.

"I always felt bad ... I never saw him with anybody."  —Gisela Casella, gunman's neighbour

Johnson also was part of a community of bird watchers and photographers who document hawks and other wildlife living in Central Park, a few blocks from his home.

In one email to another bird watcher who works at The Associated Press, Johnson wrote tenderly about spending a winter night watching ducks in the park.

"Near midnight by the Harlem Meer I watched a little 'flotilla' of Mallards swimming and softly honking … fifteen degree temp and they were carrying on unfazed. Just remarkable," he wrote.

His photographs of Central Park's hawk population appeared regularly on blogs tracking the birds.

A neighbour who often saw the 58 year old said he was always alone.

"I always felt bad," said Gisela Casella, who lived a few floors above Johnson in a modest apartment building on the Upper East Side. "I said, 'Doesn't he have a girlfriend?' I never saw him with anybody."

Victim was outgoing family man

Ercolino, 41, was described by his relatives as the opposite of a quiet loner.

His eldest brother, Paul Ercolino, said he was a gregarious salesman who often travelled, had a loving girlfriend and was the life of any family gathering.

"He was in the prime of his life," he said. "He would do anything for anybody at any time … He was so wonderful with my children. At Christmastime, he was the one who always had the best presents for the kids."

"He was in the prime of his life." —Paul Ercolino, victim's brother

Paul Ercolino said his brother, known to nieces and nephews as Uncle Ducky because of his nearly blond hair, had followed his father into the garment industry after growing up in Nanuet, just north of New York City, then later worked in women's handbags and accessories.

He said his brother had never mentioned to the family that he had any problems with a co-worker.

Company silent on deadly encounters

Hazan Import Corp. executives didn't return phone calls seeking comment Friday.

Johnson, after waiting for Steve Ercolino to come to work, walked up to him, pulled out a .45-calibre pistol and fired at his head, police Commissioner Ray Kelly said.

After Ercolino fell to the ground, Johnson stood over him and shot four more times, a witness told investigators.

"Jeffrey just came from behind two cars, pulled out his gun, put it up to Steve's head and shot him," said Carol Timan, whose daughter, Irene Timan, was walking to Hazan Imports at the time with Ercolino.

Startled New Yorkers later looked up from their morning routines in the crowded business district to see people sprawled in the streets bleeding and a tarp covering a body in front of the tourist landmark.

"I was on the bus, and people were yelling 'Get down! Get down!" accountant Marc Engel said. "I was thinking, 'You people are crazy. No one is shooting in the middle of midtown Manhattan at 9 o'clock in the morning."'