The NTSB may have evidence that he flew into the clouds intentionally.
Do you know if the aircraft had a cockpit voice recorder?
When I was a crewchief on Huey’s, we were low level fly in the mountains and bumped into a cloud bank at the top of a rising canyon. Everyone except for me was IMC... As we did a return to target maneuver, I was facing straight down and could still see the ground. We weren’t doing no 165kts! I can tell you that. Maybe 60kts.