Investigators are trying to find out why a gunman killed 13 people at an immigration centre before apparently shooting himself.
The killer - believed to be a Vietnamese immigrant - barricaded the back door of the building in New York state before opening fire on a room full of immigrants taking a citizenship class.
Many more were wounded after the rampage at the American Civic Association centre in Binghamton, about 150 miles north west of New York City.
The suspect was carrying identification with the name of 42-year-old Jiverly Voong of nearby Johnson City, a law enforcement official said, but the name was believed to be an alias.
Detectives said they had yet to establish a reason for the massacre, but according to Congressman Maurice Hinchey, whose congressional district includes Binghamton, the gunman had recently been let go from IBM. IBM did not immediately confirm the claim.
New York governor David Paterson said it was a "tragic day for New York" while President Barack Obama - speaking from Baden-Baden in Germany - condemned the "senseless act of violence".
Police chief Joseph Zikuski said the gunman parked his car against the back door "making sure nobody could escape", then stormed through the front, shooting two receptionists apparently without a word.
The killer, thought to be in his 20s, then entered a room just off the reception area and fired on a citizenship class.
One receptionist was killed, while the other, who was shot in the stomach, pretended to be dead, then crawled under a desk and called authorities, he said. The rest of those killed were shot in the classroom.
The man believed to have carried out the attack was found dead with a self-inflicted gunshot wound in an office, a satchel containing ammunition slung around his neck, authorities said.
