The Deschutes County Sheriff’s Office confirmed Thursday that the explosion of a World War II-era tank destroyer that killed two men was the result of the artillery gun being fired.

Steve Preston, 51, and Austin Lee, 22, both of Oregon City, were killed in the explosion Tuesday near a public shooting range off U.S. Highway 20 east of Bend.

Investigators are still trying to determine why firing the gun caused the tank destroyer to explode, according to a news release from the sheriff’s office.

The Oregon State Medical Examiner has finished conducting autopsies and is expected to complete a final report soon. The Deschutes County District Attorney’s Office is reviewing the case.

Preston spent several years restoring the 1944 M-18 Hellcat tank destroyer after purchasing it for $60,000 in 1999. He was part of the Military Vehicle Preservation Association and owned Sergeants Towing in Portland.

Lee, who graduated from Oregon City High School in 2011, was known for his interest in World War II uniforms and weapons. He attended Clackamas Community College from 2008 to 2010.

The sheriff’s office said Thursday that the explosion is still being investigated. Search and rescue volunteers conducted a grid search at the scene and helped locate and collect evidence.