OP - Best of luck and so sorry for your loss. I hesitate to write this because I don’t want to add to the emotional toll, but feel like I need to share this story with you.
Years ago, I had a roommate have her car stolen. Turned out it was a co-worker who took the keys out of her purse after she had just driven the co-worker to lunch that day. She barely mentioned in passing how she thought it was odd how much her co-worker was complimenting her car and later that day had an odd interaction with the same co-worker at her desk, but immediately dismissed the idea of her as a suspect as ridiculous. I pushed her to check it out. We looked up her address, drove to the house, and there in the driveway was her stolen car.
I’m not saying this was the same deal but it sure sounds like an inside job. (That or a towing mixup, as others have mentioned, but I suspect you have ruled hat out from the tracks in the snow. ). If you have even the slightest suspicion, follow up on it. Trust, but verify, and don’t feel guilty about doing so. Nice, upstanding people have a tendency not to check things out because of guilt that they are not fully trusting of the people close to them. If you have anybody close to you with substance abuse issues or money problems, you really owe it to yourself to verify. Otherwise good people get themselves in situations where they justify terrible behavior.
Are all the known keys/remotes accounted for? If you are traveling and some are at home, have someone you completely trust (a catch 22 I know), verify for you.
Again, I hope the thoughts above don’t add to what is surely a tough time emotionally. Best wishes to you.