Jiverly Wong was upset over losing his job at a vacuum plant, didn't like people picking on him for his limited English and once angrily told a co-worker, "America sucks."

It remains unclear exactly why the Vietnamese immigrant strapped on a bulletproof vest, barged in on a citizenship class and killed 13 people and himself, but the police chief says he knows one thing for sure: "He must have been a coward."

Jiverly Wong had apparently been preparing for a gun battle with police but changed course and decided to turn the gun on himself when he heard sirens approaching, Chief Joseph Zikuski said Saturday.

"He had a lot of ammunition on him, so thank God before more lives were lost, he decided to do that," the chief said.

Police and Wong's acquaintances portrayed him as an angry, troubled man who struggled with drugs and job loss and perhaps blamed his adopted country for his troubles. His rampage "was not a surprise" to those who knew him, Zikuski said.

Wong, who used the alias Jiverly Voong, believed people close to him were making fun of him for his poor English language skills, the chief said. But police said the motive still wasn't clear.

Until last month, he had been taking classes at the American Civic Association, which helps immigrants assimilate.

Then, on Friday, he parked his car against the back door of the association, burst through the front doors and shot two receptionists, killing one, before moving on to a classroom where he claimed 12 more victims, police said.

The police chief said that most of the dead had multiple gunshot wounds. Wong used two handguns for which he had obtained a permit more than a decade ago.

The receptionist who survived, 61-year-old Shirley DeLucia, played dead, then called 911 despite her injuries and stayed on the line while the gunman remained in the building.

DeLucia was in critical condition Saturday. The police chief said she and three other shooting victims were all expected to survive.

Wong's tactics — including the body armor and copious ammunition — fit him into a category of killers called "pseudo-commandos," said Park Dietz, a criminologist and forensic psychiatrist at UCLA who analyzed the Columbine High School shootings in Colorado in 1999.

Barricading the back doors to trap his prey "was his way of ensuring that he could maximize his kill rate," Dietz said. "This was all about anger, paranoia, and desperation."

The road that took Wong to his demise in a classroom at the American Civic Association in downtown Binghamton began 41 years ago and half a world away in Vietnam, where he was born into an ethnically Chinese family.

He moved to the States in the early 1990s and soon afterward became a citizen, friends and relatives said. He worked at IBM for a time, friend Hue Huynh said, but decided to move to California.

There, he worked for seven years at a caterer called Kikka Sushi, eventually making $9 an hour, said Paulus Lukas, the company's human resources manager.

"He was really good at doing his job — we respected him for that," Lukas told the Los Angeles Times. "He's never late, he's always punctual. And when he finishes his job, he goes home. He doesn't complain, he doesn't argue with people. He gets along."

But one day he simply didn't show up for work, Lukas told the Times. Early last year, he called asking the company to send his tax forms to a New York state address.

Back in New York, he apparently worked at the Shop-Vac plant in Binghamton. Former co-worker Kevin Greene told the Daily News of New York that Wong once said, in answer to whether he liked the New York Yankees, "No, I don't like that team. I don't like America. America sucks."

The plant closed in November, and Wong was out of a job. That's apparently when things really started to go downhill.

"People who end up doing this particular thing have an accumulation of stressers in their lives, and ultimately there is the one that broke the camel's back," Dietz said. "Job loss is one of the big ones, and those stressers are happening more often this year."

Huynh, the 56-year-old proprietor of an Asian grocery store in Binghamton frequented by the gunman's sister, ran into Wong at the gym recently and noted that he was complaining about how he couldn't find work.

His unemployment benefits were only $200 a week, and he lamented his bad luck, she said.

"He's upset he don't have a job here. He come back and want to work," Huynh said. Her husband tried to cheer him up by saying that he was still young and had plenty of time to find work.

Wong's story is similar to how friends were describing the recent trials of a man accused of opening fire on Pittsburgh police officers during a domestic dispute Saturday, killing three of them. They said he had recently been upset about losing his job; police say that, like Wong, he was wearing a bulletproof vest.

The Binghamton police chief said Saturday that those who were close to Wong weren't surprised to see his eventual meltdown.

A woman reached at the home who identified herself as Wong's sister told The Associated Press late Friday she did not believe he was the gunman. "I think somebody involved, not him," she said.

That's not an unusual response, Dietz said.

"What will be revealed if the investigation goes deep enough is that many people in a shooter's world knew that he was angry, mad, unreasonable, scary at times, and recently some of them came to learn that he was threatening and armed," said Dietz, who is not involved in the Binghamton investigation.

"They've known that for a long time, but none of them did what they should have done with that information."

State police got tips suggesting that Wong may have been planning a bank robbery in 1999, possibly to support a crack-cocaine addiction, Zikuski said. But the robbery never happened, and Zikuski had no other information.

Wong's father was well-known in the Binghamton area through his work years ago at the now-defunct World Relief Organization, helping recent immigrants find a doctor and obtain food stamps.

"Everyone, when they come to America, he's the one who helps," said Ty Tran, who came to the United States in 1990.

Mark Preston, 48, a neighbor of the gunman in Johnson City, outside Binghamton, said people in the family keep to themselves but often tended the bushes in their yard.

"They grow great vegetables and roses," he said.

 The police chief said Wong's suicide was his final act of failure.

Police believe Wong planned to go out in a blaze of glory in a gunfight with cops, but got cold feet when he heard sirens and put a bullet between his eyes.

"He must have been a coward," Zikuski said.

"We speculate that when he heard the sirens, he decided to end his own life. He was heavily armed, had a lot of ammunition on him and, thank God, before more lives were lost, that he decided to do that."