The gunman was identified by some police sources as Jiverly Voong.
According to Binghamton Police Chief Joe Zikuski, the gunman entered the one-story American Civic Association in downtown Binghamton at 10:31 a.m. today and began his shooting spree.
By 10:33 a.m., the shooting was over and 14 people -- including the gunman -- lay dead, the chief said. At least four people were listed in critical condition. Earlier, sources said as many as 26 people were wounded. Officials who initially said Voong worked for IBM and had been discharged later said they believed that was false. At IBM, there was no record that Jiverly Voong ever worked there.
"We have no idea what the motive is," Zikuski said.
Police were interviewing Voong's family members and executing a search warrant at his home in an effort to establish a motive. Officials were seen removing a gun rifle case, two hard drives, two briefcases and two brown paper bags from the home.
Police Chief: 'He Made Sure Nobody Could Escape'
Officials said Voong entered the civic association armed with two pistols -- a 9 mm and a .45 caliber handgun. A satchel around the gunman's neck carried high capacity magazines, a survival knife and a flashlight, according to police.
Voong backed his car up to the rear door of the building.
"Obviously, it was premeditated. He made sure nobody could escape," Zikuski said.
Voong then headed to the front where he allegedly began executing people.
Voong, 41, also known as Linh Phat Voong, was from Johnson City, N.Y.
Police refused offically to identify the shooter, though sources said it was Voong.
He allegedly burst into the civic center wearing a bright green nylon jacket and dark-rimmed glasses and promptly shot two female receptionists.
One woman died, but the second woman survived.
"She pretended she was dead," Zikuski said. As the gunman headed for a room off the reception area, "she crawled underneath the desk and sometime after that called us," he said.
Most of the people killed or injured were in one classroom taking a citizenship exam.
The police chief said 37 people were safely removed from the building, 26 of whom barricaded themselves in the building's boiler room.
Police arrived just two minutes after the receptionist called 911. Though the shooting lasted only minutes, it took police three hours to make sure the shooter wasn't still alive and laying in wait for more victims.
Zhanar Tokhtabayeva, a 30-year-old from Kazakhstan, told the Associated Press she was in an English class when she heard a shot and her teacher screamed for everyone to go to the storage room.
"I heard the shots, every shot. I heard no screams, just silence, shooting," she said. "I heard shooting, very long time ... and I was thinking, when will this stop? I was thinking that my life was finished."
Sister Stunned at News of Shooting
When the carnage was over, Voong's body was found on the first floor with a hunting knife jammed into the waistband of his pants.
"He shot those people? No. No," said a woman who identified herself as Voong's sister, but would not give her name when reached by ABC News.com.
She said her brother went to take classes today at the civic association and that she had not heard from him since. She said she did not know that he was involved in the shooting.
"I'm going to pass out," she said, and she hung up the phone.
A neighbor who lived on the same block as Voong and his family described the family as "quiet" and said they mostly kept to themselves.
"They were nice people," said the neighbor who identified herself only as Darlene. "They were good neighbors."
Police also contacted Voong's sister to say her brother was dead. She told police that Voong was attending language classes at the civic center. She said Voong is a U.S. citizen and has been in this country for 28 years.
U.S. Rep. Maurice Hinchey, a Democrat whose district includes Binghamton, initially told the Associated Press Voong was recently laid off from IBM in Johnson City -- but sources later told ABC News that it appeared that the Voong who worked at IBM was Henry Voong, "an older gentleman" who was believed to be the suspect's father, and that he had not been laid off.
Fred McNeese, an IBM spokesperson, said that because the police have not officially identified the shooter, the company is "unable to confirm any connection to IBM" at this time and has no other comment. Several hours after the shooting began, hostages started exiting the building and police declared the gunman dead.
By 1:30 p.m., police began escorting people out of the building, but continued to treat the building as a crime scene where the shooter might still be lurking.
Eyewitness Nick Masucci, a community college student and Binghamton resident, said he watched as many as 20 people exit the building and get patted down by police.
"They look like immigrants, lots of different cultures coming out of there. Some people are getting patted down. The police are taking a lot of precautions, they're still taking cover," he said.
Several people were removed from the building on stretchers. Others left with their hands on their heads and were searched by police.
Earlier today, police called Broome Community College to find someone who could speak fluent Vietnamese to "assist police with translation," said college spokesman Richard David.
Obama Comments on Shooting
People were told in nearby buildings to stay away from windows and Binghamton High School is under a lockdown as police use the school as a staging area. The school is a block and a half away from the shooting site.
President Obama issued a statement from the NATO summit he was attending in France.
"Michelle and I were shocked and deeply saddened to learn about the act of senseless violence in Binghamton, N.Y., today. Our thoughts and prayers go out to the victims, their families and the people of Binghamton," he said.
New York Gov. David Paterson called the shooting "the worst tragedy and senseless crime in the history of the city."
"We all just have profound sorrow and sadness," he said.Additonal reporting by ABC News' Ned Potter and Ki Mae Heussner.