IMO, he was murdered, but I don't think planned. He left belongings behind..glasses and phone. Makes me think he was going to step outside briefly.
If your going to commit suicide, i don't think a pen knife is going to be your choice and if it was a PLANNED murder, your going to bring a weapon, not just "hope" your victim has one on them. The path he drove, the ATM and gas visits..sounds like someone had him under their control and snapped.
Do we know if his work and cell phones revealed who he spoke to last?
Maybe someone met him at his office parking lot, called him down, and forced him to drive. Sad he lost his life and the family are without answers.