SEATTLE -- The National Transportation Safety Board has issued its conclusions in the crash of a helicopter from the roof of the KOMO-TV building in Seattle more than two years ago.

The crash on March 18, 2014, crash resulted in the death of pilot Gary Pfitzner and photographer Bill Strothman. It also injured several people on the ground.

Read the full NTSB probable cause report

The NTSB says the results of its investigation are inconclusive. It did determine, based on video of the accident from security cameras, that the helicopter lost some of its hydraulic strength. But because of the ensuing fire and the lack of any flight recorder, the reason for the loss of hydraulic boost could not be determined.

The investigation was a particularly technical one which is why it took two-and-a-half years to complete. It involved testing in France -- where the helicopter was designed -- and running multiple scenarios.

Investigators concluded the helicopter spun to the left, consistent with loss of tail rotor control. It made a 360-degree rotation while climbing. It then pitched down and banked right consistent with loss of main rotor control.

The helicopter hit Broad Street, resulting in a large fire.

The helicopter was an American Eurocopter (now Airbus Helicopters) AS 350 B2. It was owned by Helicopters Inc., based in Cahokia, Ill. Helicopters Inc. provides services to TV stations across the country, including KING.