But does he automatically go to Hell?
If he was posessed by a Demon, He could not have been saved since the Holy Spirit takes residence in the body of a believer and will not tolerate a demonic presence.
Therefore I would say with a high degree of certainty that Mr. Hui went to hell. the only possibility that he could have gone to heaven, was if he repented and accepted Christ as Saviour.
But I find this unlikely from the testimony of the witenesees that said he turned the gun on himself immediately after killing.