Officials said Wong 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.
Wong backed his car up to the rear door of the building.
"Obviously, it was premeditated. He made sure nobody could escape," Zikuski said.
Wong then headed to the front where he allegedly began executing people.
Wong, 41, also known as Linh Phat Wong, was from Johnson City, N.Y.
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."
When the carnage was over, Wong'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 Wong'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 Wong 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 Wong's sister to say her brother was dead. She told police that Wong was attending language classes at the civic center. She said Wong 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 Wong was recently laid off from IBM in Johnson City -- but sources later told ABC News that it appeared that the Wong 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.
The letter allegedly written by Wong points to his employment at a vacuum manufacturing company, Shop Vac Endicott.