No pics. I live in the NW corner of Washington State. From time to time I find a beetle in my bathroom. I almost always find them singly, though I’ve seen two on rare occasions. They are approximately 7mm in length, and the thorax, head, and proboscis make up about half of that length. They’re shaped a bit like this, only not nearly as big and more rounded than flat. They are dull black, with a couple of flashes of red. They seem to have rather thick shells, as they require a bit of pressure to kill and make an audible crunch.
Like this?
ETA: Oh, wait, probably too big.
It looks like that, but every one I’ve found have been 1/3 to 1/4 the length of the one in the link.
Yeah, Calosomas are usually pretty good-sized. Hmmm…well if they look pretty close to the above, you might try back-tracking that link to scan through the family carabidae in general and see if anything pops up that might fit. It’s a big family.