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 Wo