The unresponsive Cessna jet that veered off course over Washington, D.C., plunged in a “near-vertical descent” into a Virginia mountain at a “high velocity” before bursting into flames, according to a federal report released Wednesday.

The National Transportation Safety Board’s preliminary report offered few new details on the June 4 crash, which killed 4 people and caused military jets to scramble at supersonic speed to intercept the Cessna. But investigators were able to provide a more detailed timeline of the private jet’s movements before the crash.

Shortly after takeoff, pilot Jeff Hefner made contact with the Atlanta Air Route Traffic Control Center and was given clearance for higher altitude, according to audio recordings reviewed by investigators. Hefner continued to read back instructions as the Cessna was cleared for higher and higher altitudes but stopped responding after a controller tried to amend a prior altitude clearance, the report added.

The jet then flew for about two hours before plunging into a mountain near rural Montebello, Virginia, about 60 miles southwest of Charlottesville, Virginia.

The wreckage “was extremely fragmented, scattered around a main crater, and evidence of a post-impact fire was observed,” according to the report. Investigators were unable to find a cockpit voice recorder or flight data recorder at the crash site.

A final report that will provide details and conclusions about the accident, including probable cause, will likely take at least 12 to 24 months to complete.

A sonic boom over Washington:Breaking down the Cessna 560 Citation plane crash in Virginia

Timeline of Cessna’s movements

The Cessna had departed from Elizabethton, Tennessee, at 1:13 p.m. and was headed to Long Island Mac Arthur Airport in New York, according to the report.