The FBI said Saturday that two other planes were in the area when hijacked United Flight 93 rammed into a field in western Pennsylvania but had nothing to do with the crash.

The revelation came a day after a Defense Department official said that the military had been monitoring the plane and was in a position to intercept it. Some witnesses had claimed seeing a military aircraft in the area shortly after the crash.

FBI Special Agent Bill Crowley said Saturday that a civilian business jet flying to Johnstown -- about 20 miles north of the crash site -- was within 20 miles of the low-flying airliner, but at an altitude of 37,000 feet.

Officials Crowley didn't identify asked the business jet's pilot to descend to 5,000 feet -- an unusual maneuver -- to help locate the crash site for responding emergency crews. That could explain why some witnesses have said they saw another plane in the sky shortly after Flight 93 crashed about 10 a.m. Tuesday in a grassy field about 80 miles southeast of Pittsburgh, killing all 45 aboard.

"It's obvious a lot of people would have seen" the business jet, Crowley said.

Crowley also said there was a C-130 military cargo aircraft about 17 miles away flying at 24,000 feet when Flight 93 crashed. The military plane had no weapons on board. Crowley said he did not know where it was coming from or going, but said its crew reported seeing smoke or dust near the crash site.

Crowley didn't say what, if anything, people on the business jet saw, declining to identify them or the owner of that plane.

On Friday, Deputy Defense Secretary Paul Wolfowitz said that the military had been monitoring the plane. But Wolfowitz echoed other officials aware of cellular phone calls made by passengers to the families, who -- told by relatives that other planes had crashed into the World Trade Center towers -- said they planned to take action against the terrorists.

"I think it was the heroism of the passengers on board that brought it down, but the Air Force was in a position to do so if we had had to," he told PBS's "NewsHour With Jim Lehrer."

Also Saturday, Crowley said no indications of a bomb have been found, but it was too early to rule that out. One of the passengers who called relatives said that the hijackers claimed to have a bomb.

Most of the plane's debris was found in a crater in this rural area. While singed papers and other light debris were found up to eight miles away, Crowley said such materials could easily have been carried on the wind.

State police said eight family members of a victim or victims visited the crash site Friday, leaving flowers, photos and a U.S. flag on a hill overlooking the site. Officials said family members of 28 victims hoped to visit the site, but it was not immediately known if that occurred.

Family members were staying at Seven Springs Mountain Resort in Champion, about 20 miles west of the crash site. Although a room was prepared for them to address the media, none has opted to do so.

Meanwhile, the painstaking search for crash debris and human remains continued.

Workers are using heavy equipment to scoop dirt from the site, and then box strainers to sift through each shovelful individually, in a site marked into 20-foot-square grids, Crowley said.

Recovery teams found the plane's cockpit voice recorder just after sundown Friday. Investigators believe it may reveal an attempt by passengers to wrest control of the aircraft from hijackers shortly before impact.

The crash was the last of four that toppled the twin towers and damaged the Pentagon. Some have speculated that the four hijackers planned to target Camp David in Maryland, the Capitol or even the White House.

The voice recorder, which was found about 25 feet below ground in a crater left by the plane, was sent to a National Transportation Safety Board laboratory in Washington. The plane's flight data recorder was discovered Thursday