You guess you'll have to do something with the body now. Maybe a funeral? That sounds like the perfect way to say goodbye to an old friend. But the environment outside isn't particularly hospitable for a burial these days. It also sounds kind of depressing to host a funeral by yourself.
It's probably best to just send him back to where he came from. Years ago, when you were exploring the lab, you found a machine somewhat similar to the ectobiology equipment. Without knowing what it did, you activated it, and out came this friendly cat in a handsome little suit. You still aren't sure where he came from, though given the timestamp and coordinates on the machine, you have a feeling he belonged to your mother. If that is true, you feel bad about stealing her cat, let alone killing him. But you could never bring yourself to send him back. Until now, of course. She would probably want to know what happened to her disappearing cat, even if it meant discovering him dead a little while later.
The device uses huge amounts of power. Its entire power supply was almost fully depleted using it the first time. You've stockpiled as much uranium as you could for another test run. Looks like this will be it.