The police helicopter involved in a crash that killed two Virginia state troopers near Charlottesville earlier this month had previous mechanical problems.

The fatal helicopter crash coincided with the violent protests in Charlottesville, though the cause has not been identified. According to the National Transportation Safety Board (NTSB), the Virginia State Police-owned helicopter was sent to monitor the protests on August 12 and crashed shortly after leaving the scene. There was a post-crash fire, but no distress call was made from the helicopter.

Two state troopers were in the Bell 407 helicopter, Lt. H. Jay Cullen and Trooper Berke M. M. Bates. Both died on the scene, reports the New York Times. 

Citing NTSB records, WTOP reported that the helicopter, manufactured in 2000, sustained substantial damage in 2010. The helicopter was being used for training when it suffered an engine failure, which prompted an emergency landing.

The NTSB is working with Virginia State Police to conduct an investigation of the crash, which is expected to last 12-18 months.