WASHINGTON — The pilot of a private plane that slammed into rugged Virginia terrain, killing all four people on board, was spotted slumped over in the craft by fighter pilots who scrambled to intercept the plane as it flew over Washington, D.C., an official said.

The Cessna, chased by military jets before it went down Sunday, took off from Elizabethton, Tennessee, at 1:13 p.m. ET before air traffic controllers radioed at 1:28 p.m. asking it to stop its climb at 33,000 feet, a senior government official said.

The plane, headed northeast toward Long Island, New York, turned around near New York City and was headed back south when fighter jets from Joint Base Andrews, Maryland, were sent to investigate and spotted the pilot slumped over, the official said.

The plane ran out of fuel and crashed near Montebello, Virginia, at 3:32 p.m. The pilot was silent and out of communication with air traffic controllers in the final two hours of the flight, the official said.

On Monday, John Rumpel, whose corporation is the registered owner of the aircraft, identified three of those on board: Adina Azarian, 49; her daughter Aria, 2; and pilot Jeff Hefner.

Rumpel said he wasn’t entirely clear on the name of the fourth person, who he said worked as a nanny taking care of the 2-year-old. He described Azarian as a former employee whom he and his wife, Barbara, adopted as a daughter when she was 40 years old.

“You cannot imagine the pain,” he said.

The jet owner, whose Melbourne, Florida corporation is listed as an auto sales business, said they lost a daughter years ago, when she was 19.

Barbara Rumpel said, “We are devastated by this horrible tragedy.”

In Virginia, the crash scene is in a “densely wooded, remote, mountainous area of Augusta County, near the Nelson County line,” more than a mile from the Blue Ridge Parkway, State Police spokesperson Corinne Geller said.

First responders could not reach the scene by foot until about 8 p.m. Sunday, Geller added.

It could be days before National Transportation Safety Board investigators corral the highly fragmented debris field, the agency said.

“Everything is on the table until we slowly and methodically remove different components and elements that will be relevant for this safety investigation,” NTSB investigator Adam Gerhardt said.

The NTSB is leading the investigation. Officials arrived at the crash site near Montebello on Monday to “begin the process of documenting the scene and examining the aircraft,” the agency said in a statement.

The North American Aerospace Defense Command, known as NORAD, said F-16 fighter aircraft intercepted the plane after it was seen flying off course over the U.S. capital area. They tried to make contact with the pilot repeatedly using flares until just before the plane crashed near George Washington and Jefferson National Forest.

NORAD said a sonic boom “may have been heard by residents of the region.” The sound was reported around 3 p.m. to local law enforcement agencies and on social media throughout the Washington-Northern Virginia-Maryland area.

Pilots from the Capital Guardians, a unit of the 113th Wing of the D.C. National Guard, found that the pilot was incapacitated, a senior government official said.

It was still not clear what might have incapacitated the pilot.

“The whole 180-degree turn around New York and then tracking directly over Washington, D.C., that sounds very odd to me,” NBC News aviation analyst Jeff Guzzetti said.

Sunday’s crash immediately led Guzzetti to think of the 1999 Learjet crash that killed professional golfer Payne Stewart. All on the craft were incapacitated by lack of oxygen.

“It’s reminiscent of some sort of mechanical malfunction with the pressurization of the aircraft, which would lead the occupants to become incapacitated because of a lack of oxygen,” Guzzetti said.

Jay Blackman reported from Washington, Chantal Da Silva from London and David K. Li from New York.

Tom Costello, The Associated Press, Dennis Romero and Valeriya Antonshchuk contributed.