NEW YORK (AP) -- A trail of possible clues stretched from New York to Washington after a bicycle-riding bomber struck the landmark Times Square military station, injuring no one but scarring one of the world's most recognizable locations.
Authorities were probing whether the blast Thursday was connected to mysterious letters that arrived the same day at Capitol Hill offices, and investigators were examining strikingly similar bombings at two foreign consulates in Manhattan in the last three years. Authorities also were scrutinizing surveillance video and forensic evidence.
The Times Square bomb, contained in a metal ammunition box, produced a sudden flash and billowing cloud of white smoke. When the smoke cleared, there was no serious damage, nor any clear indication of a motive.
But like similar attacks in 2005 and last year on the British and Mexican consulates, the explosion frayed nerves of New Yorkers and tourists alike. It also heightened speculation that all three incidents were the work of a lone bomber who, perhaps emboldened by his past attacks, sought out the bright lights of Times Square.
"Times Square is `the crossroads of the world,' and we're concerned about it," Police Commissioner Raymond Kelly said at a news conference.
Capitol police, the FBI and the U.S. Postal Inspection Service were investigating the letters sent to Capitol Hill offices. The letters included a photo of the recruiting station and the claim "We Did It," according to a Democratic aide who spoke on condition of anonymity because the matter is under investigation. The message was accompanied by what appeared to be a political manifesto railing against the Iraq war, and a booklet.
Capitol police said the envelopes went through the standard security process, which involves radiating incoming mail. It can easily take a week or more, making it likely the letters were mailed well ahead of the bombing.
The blast left a gaping hole in the recruiting station's front window and shattered a glass door, twisting and blackening the building's metal frame. Guests at the nearby Marriott Marquis said they heard a bang and felt the building shake.
Police released a private security video showing a figure riding along a traffic island in the glow of Times Square's neon signs at about 3:38 a.m and getting off the bike just outside the recruitment center. About two minutes later, the cyclist rides away. Then the explosion occurs.
The images were too murky for police to get a clear description of the cyclist. But investigators were studying other security videos, including one showing a man exiting a subway station about 10 blocks away, carrying a bicycle, police said. The FBI was analyzing forensic evidence collected at the scene, Kelly said.
The commissioner cited other possible clues: a new bike discovered at about 7 a.m. in a trash bin a few blocks from the blast, and the sighting of a man on a bike near the scene moments before the explosion.
The man caught a witness' attention because he was riding slowly, wearing a backpack and a hooded jacket, Kelly said. The witness, who was buying a newspaper at the time, said the hood "pretty much covered" the rider's face.
The blast bears a striking resemblance to the two consulate explosions.
In October, two small explosive devices were tossed over a fence at the Mexican Consulate, shattering some windows; police said they believed someone on a bicycle threw the devices.
At the time, police said they were investigating whether it was connected to a nearly identical bombing at the British consulate on May 5, 2005. No one was arrested in either incident.
Those bombings involved dummy hand grenades packed with black powder as an explosive, Kelly said. He said investigators were working to determine whether similar powder was used in the Times Square blast, but he noted that the explosive used Thursday was carried in an ammunition box, rather than a grenade.
Similar ammunition boxes are readily available in Army-Navy surplus stores, Kelly said.
In another sign that the three blasts may be related, all occurred between 3:30 a.m. and 4 a.m.
The previous episodes generated nowhere near the response that the Times Square blast did. Kelly, Mayor Michael Bloomberg and the top FBI official in New York appeared at a nationally televised news conference in Times Square, and presidential candidates issued statements condemning the blast.
Bloomberg said the act "insults every one of our brave men and women in uniform stationed around the world."
Associated Press writers Matt Apuzzo in Washington and Ula Ilnytzky in New York contributed to this report.
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