where did you buy him from? also do you know if he was captive bred or wild caught? I doubt mouse size killed your snake, you'd be amazed at the size of prey they can take down. The hatchlings I have even at 49 grams could take down a full grown mouse with no issue. Did you see mites on your snake? When it comes to cleaning I would use diluted bleach, go to paper towels and keep the tank very basic until you are done with your quarantine of the animal. I would have a water bowl and two hides, one on each side of your tank. Have a hot spot of about 92 and air temp around 83-85, I also keep my humidity around 60%. Hope this helps some, just be careful who and where you are buying from. A lot of petstores animals have mites.