There was no distress call, according to federal safety investigators looking into what caused a helicopter crash that killed two Virginia State Police officers as they were conducting surveillance work during the white nationalists' rally in Charlottesville on Saturday.

Lt. H. Jay Cullen and Trooper Berke Bates were killed in the crash. According to investigators with the National Transportation Safety Board, the helicopter left Charlottesville airport around 3:54 p.m. and was conducting surveillance over the downtown area. It left downtown Charlottesville at around 4:42 p.m. to provide support for Virginia Gov. Terry McAuliffe’s motorcade. Roughly two minutes later, at 4:44 p.m., officials received the first 911 call reporting the crash, reports the Washington Post .

According to the report, the helicopter’s vertical flight path was about 45 degrees when it descended into trees. Investigators said the main wreckage was about 100 yards from where the aft portion of the tail boom became lodged in a tree.

Investigators said that the helicopter was traveling about 34 miles per hour at an altitude of 2,300 feet. The crash occurred in a wooded area on Old Farm Road in Albemarle County, about seven miles southwest of the Charlottesville airport. There was a post-crash fire, investigators said.

Lt. Cullen was a veteran Virginia State Police trooper who had nearly 20 years of experience flying helicopters and airplanes for the department’s aviation unit. Trooper Bates paid his way through aviation school last year in hopes of fulfilling his lifelong dream of flying for the State Police. Bates would have turned 41 on Sunday, reports the New York Times .

Cullen is survived by a wife and two sons. Bates is survived by his wife and their son and daughter, 11-year-old twins.

The full investigation into the deadly crash is expected to take 12 to 18 months.