Giuliani: Recovery, cleanup could take a year

A police officer uses a dog to search the rubble of the World Trade Center.

NEW YORK (CNN) -- Tons of rubble and a host of structural, logistical and safety challenges could extend recovery and cleanup efforts in Lower Manhattan at least a year, Mayor Rudy Giuliani said Friday.

Workers already have removed around 134,000 tons of debris from around the World Trade Center complex, but more than 1 million more tons of rubble remain.

"The amount of time they will need to remove and clear the site will range anywhere from nine months to one year because of the complexity they believe they will face," Giuliani said.

The most difficult task, the mayor explained, could come after workers remove all the surface material and debris from the site, which includes the wreckage of the two 110-story towers. Their collapse drove some of the structures and material deep into the ground, he said.

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Meanwhile, New York Police Commissioner Bernard Kerik said the Organized Crime Control Bureau and the Trade Waste Commission are investigating the theft of debris from the disaster site. The stolen material was taken to two locations in New Jersey and one in Long Island, and Kerik said police have not established a motive.

The official number of people missing in the rubble dropped to 5,960 on Thursday after a recheck of missing persons reports, Giuliani said. The police department is drawing its numbers from six different sources, meaning there is the possibility of duplication.

The mayor said 306 deaths have been confirmed, and 238 of the dead have been identified.

Dr. Robert Shaler, chief of forensic biologist in the New York City medical examiner's office, told The Associated Press that most victims examined died from "blunt trauma," and others from burns, smoke inhalation and injuries from sharp debris.

Giuliani said he attended the wakes of three firefighters Thursday night and hoped to attend at least eight upcoming funerals, praising the thousands of people who also have turned out to honor the dead and comfort their families.

"I was really very, very much impressed and strengthened by … the turnouts, " the mayor said. "It was very comforting for the families to be able to see thousands of people showing up out of respect."

A total of 8,786 people have reported injuries from the September 11 attacks on the World Trade Center, Giuliani said.

The mayor dismissed concerns about air quality near the World Trade Center, which contained asbestos.

"Although they occasionally will have an isolated reading with an unacceptable level of asbestos … it's very occasional and very isolated," Giuliani said. "The air quality is safe and acceptable."