Leads in Times Square bombing fizzle

NEW YORK (CNN) -- Investigators trying to track down the person who set off a small bomb in front of a military recruitment center in Times Square have dismissed one lead and are casting doubt on another.

The person who sent letters to members of Congress that included a photo of the recruitment station "is not the bomber" who attacked the building Thursday, law enforcement sources say.

"The letter's really innocuous," New York Police Commissioner Ray Kelly told CNN's "American Morning" Friday. "It's really advice to the Democratic Party as to how to win the 2008 election."

The letters drew suspicion because they were delivered to members of Congress the day of the bombing and included a picture of the recruitment station with the words, "We did it."

Kelly said the letter writer claims the picture was the writer's 2006 holiday card and the words "We did it" referred to the Democrats' takeover of Congress in that year's elections. Watch Kelly detail the investigation »

Because the letters -- full of anti-war rhetoric and sent only to Democrats -- passed through the usual congressional security screening process, they must have been mailed at least several days before the bombing, The Associated Press reported.

"There's nothing particularly threatening in the document," Kelly said.

"It's an ugly coincidence," a law enforcement source who requested anonymity said.

Meanwhile, authorities reviewing an encounter at the U.S.-Canadian border last month don't expect it to break the case, a senior U.S. official said.

In early February, a car with three people in it was stopped by Canadian authorities as it was crossing from New York into Canada, the official said.

As the car was routinely searched, a backpack with pictures of New York, including ones of Times Square and at least one showing the recruiting station, was found. Canadian authorities also found some anarchist material, the official said.

The individuals told authorities they had been visiting New York City for a week.

This official pointed out that the recruiting station is a prominent fixture in Times Square and it would be likely to appear in photos of the area.

At some point, two of the men ran away. The Canadians then forwarded the information to the NYPD liasion officer in Canada who alerted NYPD.

It was determined by the Canadians and NYPD at the time that there was no threat related to this incident, but officers at the recruiting station were informed about it, the official said.

"Our teams of detectives that go around and talk to businesses did go out and speak to the people in the recruiting station and told them about the fact that these pictures were found," Kelly said.

"So federal officials are going back to take another look, and [are] attempting to speak to Canadian officials about that stop."

The focus in the search for the bomber now returns to New York, where investigators continue to study video from security cameras in Times Square.

A video that Kelly showed reporters Thursday afternoon shows a person wearing a hood riding up to the station on a bicycle, walking up to the door, pausing for a few moments, then riding off. The explosion occurs about a minute later.

A 10-speed bike in good condition was later found in a trash bin not far from the scene. Police said they were trying to determine if it was the bicycle seen in the video.

The bomb consisted of some kind of "low-order explosive" contained in a military-style ammunition box, Kelly said.

"This was not a particularly sophisticated device," he said.

Mayor Michael Bloomberg was defiant in the wake of the blast.

"Whoever the coward was that committed this disgraceful act on our city will be found and prosecuted to the full extent of the law," Bloomberg said.

The blast is similar to two other incidents in New York, one in October and one in May 2005.

Both times, an explosive device was detonated around 3 a.m.

In the October incident, a bomb was detonated near the Mexican Consulate, shattering windows. At that time, authorities said the explosive device was similar to the ones used in a May 2005 blast at the British Consulate.

In both cases, authorities were looking for a person spotted riding a bicycle in the area.

"The times are very similar," Kelly said, referring to the hour of the blasts. "All three incidents took place with an individual on a bike, leaving a bomb. So, that's a possibility. We can't say with certainty that that's the case, but that's one of our investigative premises."

Police stopped several bicyclists for questioning Thursday morning near Times Square, but no one was detained, WABC-TV reported.

The office's front door and window were shattered by the explosion, and the door's metal frame was bent.

Recruiters will work from an office in Union Square until repairs are made, Pentagon spokesman Bryan Whitman told AP. E-mail to a friend

CNN's Kevin Bohn contributed to this report.

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