BINGHAMTON, N.Y. â The man who police say killed 13 people in a shooting rampage at an immigrant community center was depressed and angry over losing his job and about his poor English skills, officials said Saturday. Police Chief Joseph Zikuski told NBC's "Today" that people "degraded and disrespected" the gunman over his poor English. Mayor Matthew Ryan, speaking on ABC's "Good Morning America," said the man, believed to be 42-year-old Vietnamese immigrant Jiverly Voong, was angry about his language issues and his lack of employment. On Friday, he barricaded the American Civic Association community center's back door with his car, walked in the front and started shooting with two handguns. Within minutes, a receptionist, 12 immigrants taking a citizenship class and the gunman were dead. Another receptionist, who played dead after she was shot in the abdomen, called 911 to get police to the scene within two minutes. Zikuski said the injured receptionist stayed on the phone for 90 minutes, "feeding us information constantly," despite a serious wound in the abdomen. "She's a hero in her own right," he said. Four people were critically wounded in the Friday massacre, and 37 others made it out, including 26 who hid for hours in a basement boiler room while police tried to determine whether the gunman was still alive and whether he was holding any hostages, Zikuski said. Investigators said they had yet to establish a motive for the shooting, which was at least the fifth deadly mass shooting in the U.S. in the past month. The suspected killer carried ID with the name of 42-year-old Jiverly Voong, of nearby Johnson City, N.Y., but that was believed to be an alias, said a law enforcement official, speaking on condition of anonymity. The man was found dead in an office with a self-inflicted gunshot wound, a satchel containing ammunition slung around his neck, authorities said. Police found two handguns â a 9 mm and a .45-caliber â and a hunting knife. A second law enforcement official, also speaking on condition of anonymity, said the handguns were registered to Jiverly Wong, another name the man used. Both officials were not authorized to speak publicly. A woman who answered the phone at a listing for Henry D. Voong said she was Jiverly Voong's sister but would not give her name. She said her brother had been in the country for 28 years and had citizenship. Zikuski told "Today" that the shooter had worked in Binghamton for Shop-Vac, which closed in November. The sister told the AP on Friday that her brother worked at a company where "they make the vacuums." The mayor told ABC that the gunman "had lost a job recently and was somewhat angry." "He had language issues, didn't speak English that well, and was really concerned about his employment situation," Ryan said. Initial reports suggested Voong had recently been let go from IBM, which has roots in the region, but a person at IBM said there was no record of a Jiverly Voong ever working there. His father, Henry Voong, does work there. The attack at the American Civic Association, which helps immigrants settle in this country, came just after 10 a.m. as people from all over the globe â Latin America, China, Kazakhstan, Vietnam, Africa â gathered for English and citizenship lessons in an effort to become a bigger part of their new home. The gunman parked his car against the back door before barging through the front and opening fire, apparently without saying a word. He then entered a room just off the reception area and fired on a citizenship class while terrified people scrambled into a boiler room and a storage room. Abdelhak Ettouri, a Moroccan immigrant who lives in nearby Johnson City, told the Binghamton Press & Sun-Bulletin he found the back door locked when he tried to flee, then ran to hide in the basement as he heard 12 to 14 shots: "Tak-tak-tak-tak." Zhanar Tokhtabayeva, a 30-year-old from Kazakhstan, was in an English class when her teacher screamed for everyone to go to the storage room. "I heard the shots, every shot. I heard no screams, just silence, shooting," Tokhtabayeva told the AP. "I heard shooting, very long time, and I was thinking, when will this stop? I was thinking that my life was finished." Hoi Nguyen of Binghamton said his 36-year-old daughter Phuong Nguyen, who survived the massacre, was taking an English class in the basement when the gunfire started. "She said it sounded like a firecracker and everyone in the class was startled," he said. "Then the teacher locked the door, called the police, then told everyone they couldn't leave the room." Police arrived in minutes, heard no gunfire and waited for about an hour before entering the building to make sure it was safe for officers. They then spent two hours searching the building. They led a number of men out in plastic handcuffs while trying to sort out victims from the killer or killers. The police chief said the suspected gunman "was no stranger" to the community center and may have gone there to take a class. He said he had no idea what the shooter's motive was. On Friday evening, police searched Voong's house and carried out three computer hard drives, a brown canvas rifle case, a briefcase, a small suitcase and several paper bags. Dr. Jeffrey King, speaking at the Catholic Charities office, said he was certain his mother, 72-year-old Roberta King, who taught English at the community center, was among the dead. Authorities read a list of survivors and his mother's name wasn't on it, he said. The shootings took place in a neighborhood of homes and small businesses in downtown Binghamton, a city of about 47,000 situated 140 miles northwest of New York City. The region was the home to Endicott-Johnson shoe company and the birthplace of IBM, which between them employed tens of thousands of workers before the shoe company closed a decade ago and IBM downsized in recent years. A string of attacks in the U.S. in the last month left 44 people dead in all. A gunman killed 10 people and himself in Samson, Ala.; shootings that began with a traffic stop in Oakland, Calif., left four police officers and the gunman dead; an apparent murder-suicide in Santa Clara, Calif., left six dead; and a gunman went on a rampage at a nursing home Sunday, killing seven elderly residents and a nurse who cared for them.