As many as four men from Qatar are suspected of aiding the Al Qaeda hijackers in the Sept. 11, 2001, terror attacks, but investigators concluded in the days following the attacks that there was insufficient evidence to charge the suspects, law enforcement sources told Fox News on Tuesday.

Officials spoke after The (London) Daily Telegraph published leaked diplomatic cables obtained by WikiLeaks that were sent between the U.S. embassy in Doha and the Department of Homeland Security in Washington.

The documents reveal that on Aug. 15, 2001, three men from Qatar flew to the U.S. from London. They visited New York City and Washington D.C., and made trips to the World Trade Center, the Statue of Liberty, the White House and "various areas" in Virginia.

They then flew to Los Angeles where they checked into a hotel and stayed for several days, checking out on Sept. 10.

According to the memo, "hotel cleaning staff grew suspicious of the men because they noticed pilot type uniforms, several laptops and several cardboard boxes addressed to Syria, Jerusalem, Afghanistan and Jordan in the room."

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"The men had ... a cellular phone attached by wire to a computer," it added. "The room also contained pin feed computer paper print outs with headers listing pilot names, airlines, flight numbers, and flight times."

The trio was scheduled to fly to Washington one day before the attacks, but instead departed for London. A subsequent FBI investigation found that the men's airline tickets and hotel were paid for by a "convicted terrorist," the memo said.

The next day, the American Airlines flight they had intended to take to Washington was hijacked by five terrorists and crashed into the Pentagon, killing 184 people.

According to the cable, the three men, Meshal Alhajri, Fahad Abdulla and Ali Alfehaid, were helped by a fourth man, Mohamed Al Mansoori, while in the U.S.

Al Mansoori, who has never been publicly named in connection with the 9/11 attacks, is suspected of "aiding people who entered the U.S. before the attacks to conduct surveillance ... and providing other support to the hijackers."

“There was never enough evidence to bring charges against the men,” a source told Fox News, adding that “the situation smelt bad," without elaborating further.

The 9/11 Commission report, released in 2004, confirmed that at least two of the hijackers had a "brief stay in Los Angeles about which we know little."

Law enforcement sources told Fox News there was no active hunt underway for the men but at least one remained of interest to the U.S. Al Mansoori at one time lived in Long Beach, Calif., but his current location is not known.

Only one person was tried and convicted for the 9/11 attacks, Zacarias Moussaoui, a French citizen often called the "20th" hijacker. He is currently serving a life sentence in a Colorado prison.

The leaked cable was published Tuesday amid reports Al Qaeda was attempting to procure nuclear material and recruit rogue scientists in order to build a radioactive "dirty bomb."

Security chiefs told a NATO meeting in Jan. 2009, that the terror group was planning a program of "dirty radioactive improvised explosive devices [IEDs]," according to another set of documents released by WikiLeaks.

The cable, also obtained by The Telegraph, revealed that Al Qaeda documents found in Afghanistan in 2007 convinced security officials that "greater advances" had been made in bio-terrorism than was previously feared.

Fox News' Catherine Herridge contributed to this report.