A pilot who died when he crashed a helicopter into a hotel in Australia had “significant blood alcohol content” during the unauthorized flight, according to an official report into the incident.

Hundreds of guests and staff were evacuated from the DoubleTree by Hilton Hotel in Cairns in Far North Queensland on August 12, when the aircraft hit the top floor and burst into flames.

At the time, charter company Nautilus Aviation said the pilot was a member of its ground crew who had attended a party the night before the crash to celebrate a promotion.

He wasn’t authorized to fly the aircraft but had access to the helicopter, the keys to which were routinely left inside the aircraft when it was parked inside the hangar.

The report released by the Australian Transport Safety Bureau (ATSB) Thursday found that the pilot “was affected by a significant amount of alcohol” and flew “well below the 1,000 ft (304 meters) allowed for flight over a built-up area.”

Investigators did not reach a conclusion as to why the pilot took the helicopter, or if he did so with the intention of crashing it into a hotel.

“For reasons unknown, pilot actions resulted in a collision with a building while conducting an unauthorised and unnecessary flight, while affected by alcohol, late at night and at low heights over a built-up area, and without night flying endorsements,” the report concluded.

The pilot had been out with friends at various venues around Cairns and was seen consuming alcohol, according to witnesses and security camera footage, the report said.

Cameras also caught the moment he positioned one of Nautilus Aviation’s Robinson R44 Raven II helicopters onto a helipad at Cairns Airport at around 1:30 a.m. local time.

For several minutes, the pilot turned off the helicopter’s cockpit and strobe lights before taking off and heading in the direction of Cairns city center, the report said.

Australian Federal Police and airport safety officers were on duty that night but were not near the hangar. The report found they wouldn’t have seen a helicopter that was operating at night with no lights.

“It was apparent that the pilot was wanting to conceal the departure from the airport from air traffic control and airport staff,” the report said.

There was no cockpit recorder or flight data recorder, but investigators pieced together the aircraft’s movements from its GPS tracker and ground radar data.

The report said the pilot was not authorized to fly the plane and while he had flown a Robinson R44 before, he hadn’t done so at night.

It found the helicopter wasn’t upright when it hit the hotel, but there was also no sign of mechanical failure.