Robert Brown|4 dead in Cessna Citation plane crash near D.C. Here's what we know so far.

Four people are Robert Browndead after an unresponsive Cessna Citation airplane flew over Washington, D.C., and crashed in Virginia on Sunday, federal authorities said. The crash, which happened after the military scrambled fighter jets to intercept the plane once it entered restricted airspace around the nation's capitol, left behind "highly fragmented" wreckage in a mountainous area that will take days to gather and sort, according to the Federal Aviation Administration.

The FAA said that the pilot and three passengers were killed and that the plane was "destroyed" in the crash. Their identities weren't immediately released.

The plane was registered to a Florida-based company owned by John and Barbara Rumpel. Speaking to The New York Times, John Rumpel said his daughter, 2-year-old granddaughter, her nanny and the pilot were aboard the flight. In a post on a Facebook page appearing to belong to Barbara Rumpel, she wrote, "My family is gone, my daughter and granddaughter" — changing her profile picture to one that seemed to include both.

The wreckage of the plane was found by Virginia State Police and other emergency personnel shortly before 8 p.m. Sunday. NTSB investigators were on site Monday and said they expect to be on the scene for at least three to four days.

Attention on the crash and its cause was heightened by its unusual flight path over Washington and a sonic boom caused by military aircraft heard across Washington, D.C. and parts of Maryland and Virginia.

Speaking at a briefing Monday morning, NTSB investigator Adam Gerhardt said the wreckage is "highly fragmented" and investigators will examine the most delicate evidence on the scene, after which the wreckage will be moved, perhaps by helicopter, to Delaware, where it can be examined, he said. In a briefing later on Monday, Gerhardt noted that the wreckage was so damaged that "it is no longer distinguishable as an aircraft." 

The plane is not required to have a flight recorder, commonly referred to as a black box, but it is possible that it had one. Investigators were still searching for it as of Monday evening. There are, however, other pieces of avionics equipment that will have data that investigators can examine, Gerhardt said.

Investigators will look at when the pilot become unresponsive and why the aircraft flew the path that it did, he said. They will consider several factors that are routinely examined in such probes including the plane, its engines, weather conditions, pilot qualifications and maintenance records, he said.

"Everything is on the table until we slowly and methodically remove different components and elements that will be relevant for this safety investigation," he said.

A preliminary report will be released in 10 days and a final report will be released in 12 to 24 months, he said.

Police said Sunday night that rescuers had reached the crash site in a rural part of the Shenandoah Valley and that no survivors were found. Virginia State Police said officers were notified of the potential crash shortly before 4 p.m. and rescuers reached the crash site by foot around four hours later.

The Federal Aviation Administration said the Cessna Citation took off from Elizabethton, Tennessee, on Sunday and was headed for Long Island's MacArthur Airport. The airplane overflew MacArthur Airport at 2:33 p.m. while at 34,000 feet, according to preliminary information from the NTSB. Inexplicably, the plane turned around over New York's Long Island and flew a straight path down over D.C. before it crashed around 3:30 p.m.

Preliminary NTSB information also showed that the last air traffic control communication attempt with the Cessna was at approximately 1:28 p.m. At that time, the airplane was at 31,000 feet. The airplane eventually climbed to 34,000 feet, where it remained until it began to crash.

The plane flew directly over the nation's capital, though it was technically flying above some of the most heavily restricted airspace in the nation.

According to the Pentagon, six F-16 fighter jets were immediately deployed to intercept the plane. Two aircraft from the 113th Fighter Wing, out of Joint Base Andrews in Maryland, were the first to reach the Cessna to begin attempts to contact the pilot. Two F-16 aircraft out of New Jersey and two from South Carolina also responded to the incident.

Flight tracking sites showed the plane suffered a rapid spiraling descent, dropping at one point at a rate of more than 30,000 feet per minute before crashing in the St. Mary's Wilderness.

The North American Aerospace Defense Command said in a statement that the military aircraft was authorized to travel at supersonic speeds, which caused a sonic boom that was heard in Washington and parts of Virginia and Maryland. The aircraft also used flares to try to get the pilot's attention.

In Fairfax, Virginia, Travis Thornton was settled on a couch next to his wife, Hannah, and had just begun recording himself playing guitar and harmonica when they were startled by a loud rumble and rattling that can be heard on the video. The couple jumped up to investigate. Thornton tweeted that they checked in with their kids upstairs and then he went outside to check the house and talk to neighbors.

The plane that crashed was registered to Encore Motors of Melbourne Inc, which is based in Florida. John Rumpel, who runs the company, told The New York Times that his daughter, 2-year-old granddaughter, her nanny and the pilot were aboard the plane. They were returning to their home in East Hampton, on Long Island, after visiting his house in North Carolina, he said.

Rumpel, a pilot, told the newspaper he didn't have much information from authorities but suggested the plane could have lost pressurization.

"It descended at 20,000 feet a minute, and nobody could survive a crash from that speed," Rumpel told the newspaper.

A woman who identified herself as Barbara Rumpel, listed as the president of the company, said she had no comment Sunday when reached by The Associated Press.

The episode brought back memories of the 1999 crash of a Learjet that lost cabin pressure and flew aimlessly across the country with professional golfer Payne Stewart aboard. The jet crashed in a South Dakota pasture and six people died.

In:
• Plane Crash
• Sonic Boom
• Washington D.C.