BINGHAMTON, New York (CNN) -- The man suspected of killing 13 people in a shooting massacre at an immigration services center in Binghamton, New York, on Friday had a troubled past that once put him on law enforcement's radar, police say.
Police say Jiverly Wong killed 13 at a immigration services center in Binghamton before killing himself.
Police interviews with former co-workers, neighbors and acquaintances of Jiverly Wong create a murky picture of a man who struggled to master English and allegedly spoke of robbing a bank and shooting the president.
Such information provides little insight into why Wong, a naturalized U.S. citizen from Vietnam, would gun down 13 people at a center that welcomed foreigners like himself.
Wearing a bulletproof and armed with two weapons, Wong, 41, barricaded the back door of the American Civic Association with his car and burst in through the front, fatally shooting 13 people before turning the gun on himself, police said.
Wong lived with his parents in Johnson City, near Binghamton, the site of a law enforcement search on Friday. He was known to practice target shooting there, acquaintances told state police.
Less than a month before Friday's massacre, police say, Wong stopped taking English classes at the center. The ACA provides counseling, resettlement assistance, citizenship and language training to immigrants and refugees.
Wong's difficulties with English appeared to be a source of humiliation evident to people knew him.
"We picked up that people were making fun of him. He felt that he was being degraded for his inability to speak English," Binghamton Police Chief Joseph Zikuski said in a news conference.
Compounding his troubles, he lost his job at Shop-Vac Corp., where he installed motors in industrial vacuum cleaners, in November.
"He was somewhat disgruntled. He had lost a job, he was not too good at English, had some problems," Binghamton Mayor Matt Ryan told CNN. "He didn't feel people were respecting him."
Wong's former co-workers described him as an intelligent, helpful colleague who also had a dark side.
"He said he wanted to shoot the president," Donald Ackley said. "I told him the FBI was out looking for him when he said that. He went crazy over that."
Police have also learned that in 1999, New York State Police received a tip from a confidential informant that Wong had a drug habit and was planning to rob a bank.
There is no sign that Wong ever carried out the threat, but the incident put him on law enforcement's radar, authorities said.
And to those who knew him, Friday's massacre did not come as a shock, Zikuski said.
The police chief said that "some of this behavior on his part wasn't a total shock," but did not elaborate what, if any, previous behavior he meant.
"From the people close to him, the actions that he took were not a surprise to them," he said.
CNN's Allan Chernoff and Susan Candiotti contributed to this report.