It might give you immense satisfaction to torture this creature in the most agonizing way, however an even worse fate would be "entombment".

Without any anaesthetic you paralyze him so that he feels everything yet is unable to move a muscle. Then with dirty pliers, screwdrivers, and shears you remove his tongue, visual organs, auditory organs, olfactory organs, penis, hands, and feet, making sure to cauterize the wounds with red hot cattle brands, all the while keeping him alive.

Next, you slowly shove a red hot spike up his anus then whip him with the most fearsome scourge you can find until nearly all of his skin has been ruptured.

Finally, you lock him in a windowless acoustically-sealed room without heat and an uneven stone floor covered with broken glass. The only outlets are a steel grate in the floor and a faucet embedded in the ceiling that drips raw sewage 24-7.

Until he dies, which may take several days, the only things he'll be able to do is defecate, writhe on the floor in agony, and scream.

This should give him plenty of time to reflect upon the wickedness that he has done.