Then let this be its final resting place. Whether that rest is found through death, or eternal captivity. Although being trapped here all alone will be dreadfully boring... But given the nature of its crimes, perhaps it's well-deserved.

[Not like any of them have had the opportunity to talk to the big bad killer to gauge if it has sentience to understand what it has done. Mettaton can only assume that whatever it is, it thrives on killing people somehow. Which is bad.]