Authorities said Friday there was no link between a letter sent to several members of Congress that read "We did it" and the bombing of a military recruiting center in New York City's Times Square.

The person who wrote the letter is an anti-war activist and has been questioned in the Los Angeles area, law enforcement officials told The Associated Press. He sent up to 100 letters to various people in Congress and even mailed a photo of a man standing in front of the recruiting center.

"It was just an incredibly unbelievable coincidence," said one of the law enforcement officials, who spoke on condition of anonymity because the investigation in New York is continuing.

Authorities on Thursday questioned the Los Angeles area man who sent the lengthy anti-war letters, but found his mailings to be unrelated to the bombing and did not expect to bring any charges, the officials said. The notes contained no threats, and bore the words "Happy New Year, We Did It."

Laura Eimiller, an FBI spokeswoman in Los Angeles, said an individual was questioned there about the letters to Congress and "there is no evidence linking the letters, which contained no threat, to the bombing."

Some law enforcement officials said the "We did it" referred to the Democratic wins. The Democrats gained control of Congress in 2006.

"The letter is in essence advice to Democratic legislators. It's innocuous," said New York City Police Commissioner Ray Kelly. "It's the type of thing you hear on television all the time. ...The FBI questioned this individual yesterday and they pretty much discounted it."

But though there wasn't a link to the Times Square blast, the investigation into the letters is ongoing, Capitol Hill sources told FOX News.

Democratic lawmakers on Capitol Hill were startled to receive the notes in their office mail Thursday afternoon, just hours after the early morning New York bombing, and turned them over to the Capitol Police.

In a phone interview with WNYW-TV in New York, the top Republican on the House Homeland Security Committee, Rep. Pete King (R-NY), said more letters could be discovered Friday morning because of the sheer number that was sent.

Meanwhile, law enforcement officials were investigating whether the explosion was connected to strikingly similar bombings at two foreign consulates in New York.

And authorities were revisiting a recent incident last month involving four men who tried to flee a checkpoint at the border with Canada when Canadian officials attempted to question them, according to Kelly.

Two of the men got away, leaving behind a backpack that included photos of locations in New York City, including the recruitment center at Times Square, the commissioner said.

Investigators continued to scrutinize surveillance video and forensic evidence after an apparent bicycle-riding bomber struck the landmark station Thursday, scarring one of the world's most recognizable locations.

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," Kelly said at a news conference.

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.

Click here for more on the bicyclist caught on surveillance video.

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.

At Times Square on Friday, there were tourists snapping pictures, pedestrians bustling about — and a sense of firm resolve among the military people who were guarding the mangled recruiting station in the middle of a traffic island near the city's famed Theater District.

"I hope that people see that nothing affects us. They can bomb the place, protest, but we're going to continue recruiting," said Sgt. 1st Class James Latella.

Jessica Lindsey, 30, of Pensacola, Florida, paused for pictures with friends in front of the recruiting station during their shopping expedition and birthday celebration.

"We were nervous about coming here and staying across the street," but hotel workers assured them everything was fine, she said.

FOX News' Chad Pergram, Trish Turner and The Associated Press contributed to this report.