If the reason he was not wearing a helmet was because someone stole it and he was trying to get home, whoever stole it needs to be caught and charged with murder. I don't see this being any different than when someone runs from the cops, the cop looses control and kills someone, then the person that ran is charged with murder. A crime can be directly connected to this riders death, so the person that committed that crime should be charged with murder.
Even if the wreck looks bad enough where he wouldn't have survived with a helmet, who knows if the wreck would have happened in the first place if he had his helmet. Maybe the wreck happened because he was distracted or uncomfortable because he was not used to riding without a helmet.
Too sad... RIP to the rider. I didn't even know him and I am ready to go after whoever stole his helmet. My prayers are with his family.