The incident occurred as U.N. Secretary-General Kofi Annan was meeting with Glafkos Clerides, the Greek Cypriot leader, and Raouf Denktash, the Turkish Cypriot leader, in his 38th floor offices on the east, or opposite, side of the building.
Also, Hans Blix, executive director of the U.N. Monitoring, Verification and Inspection Commission for Iraq was briefing the Security Council, also on the east side of the complex.
At least one window was seen to have been broken on the secretariat's west side. Witnesses said the gunman scattered a few dozen sheets of paper between the vehicle entranceway and a large circular fountain in front of the building. Security officers quickly collected the handwritten papers.
"It was a rambling message on political rights in North Korea," Chief Michael McCann of U.N. Safety and Security later told reporters. He said the suspect, Steve Kim, born in 1945, was removed from the U.N. headquarters complex in the custody of the FBI, about 90 minutes after the 1:10 p.m. EDT incident.
Kim was armed with a seven-shot, .357 Magnum with a 4 inch barrel, McCann said.
A spokesman for the New York office of the FBI, James Margolin, said Kim was a naturalized U.S. citizen from Korea, but did not know if he came from the north or south of the peninsula.
He said Kim faces possible charges under the Protection of Foreign Officials Act, weapons possession and criminal trespass.
Members of the U.S. Secret Service, U.S. State Department security and officers of the New York Police Department detailed to protect principals in the Cyprus talks apprehended the Kim, McCann said. They were waiting in the traffic circle when the incident occurred behind security officers at the guardhouses.
Since U.S. law enforcement nabbed Kim, McCann explained, the U.S. government was bringing charges even though the incident occurred on the international territory of the United Nations.
An announcement to building occupants said the gunman "jumped the fence," which is about 6 feet high, running along First Avenue on Manhattan's East Side.
McCann said he entered the complex north of the main 43rd Street pedestrian and vehicle entrance, where a thigh-high fence, grass area, bushes and a concrete wall span the two blocks to the next guard house north, at 45th Street, across First Avenue from the U.S. Mission to the United Nations.
From video images obtained by CNN recording the arrest of the middle-aged suspect from its fourth floor office, it appeared he was of Asian origin and was dressed in a dark blue, waist-length jacket and military-green trousers. He appeared to offer no resistance.
Hua Jiang, Annan's deputy spokesman, said she heard a shot and looked out her third floor window, overlooking the plaza in front of the secretariat.
"There was this guy with a gun shooting in the air for several shots, I think about six shots," she said. "After that he threw the gun down and within seconds security was there and they overpowered him and took him away."
Hua pointed out that the incident occurred near an unused guard shack at the side of the First Avenue double drive entrance-exit-gate, itself dominated by a recently built high-tech guardhouse. Guards were under instructions to remain at their entrance-way posts in case of emergencies.
She said the drive gates were closed at the time.
McCann said his officers were armed and authorized to use deadly force to stop assailants. He also said that since Sept. 11, 2001 security arrangements have been under review and various U.N. bodies were considering requests for improvements. A few of the 36 additional security officers approved for the complex have been hired.