Is a car which belonged to a decedent with an unsettled will technically stolen if taken across state lines by the executor?

My grandfather passed away last month and it quickly became apparent that my father, the executor, had no intention of living up to his fiduciary duty. Over a month later he still hasn't filed the will with the relevant court, didn't notify his bank or investment firm, and hastily drove a car of his back to his home state of California. I wonder if I can report this car as stolen since my grandfather's assets haven't been disbursed yet, beneficiaries haven't been notified and the probate process hasn't even been initiated.