” records from both phones”
If he killed her, which he probably did, he must likely has both phones, or disposed of hers. Not a lot of help.
The car GPS would be good.
records are kept on the carrier end.
heck my android phone has (had. I keep location off now) a list of all the places I have been on google servers.
you don’t need the phone. you need the cooperation of the carrier or manufacturer.
they will know the last location of the phone and have a really good bread crumb trail to follow.
that smart phone is to smart to let you get away with murder if you bring it along and powered on.