wow that's a tough situation. Kudos for handling it well.
You are trying to be humane and you've done a good job. I too have used release traps for a mouse at one point.
But I'm not convinced you can know for certain why the mouse was in that state. ...I think if it were me I'd still bring them outside near a tree or something. It would bother me though and I agree it's a sad thing
. I'd be curious to know what others might suggest.