Gmail hacked stolen by thief ex girlfriend

Hello,
My brother in law had his LG tablet stolen by a ex girl friend who lied an keep him high ..he's now with family going to rehab..
She stole an sold his tablet say he lost it at the time he had a fido account he at the time received a message on his phone about his password he was high but questioned her with a brush off an it's nothing here's more drugs.. the password was changed the recover number all means to recover was changed.. he received a bill 500 dollars ..the person she sold it to called people the tablet plan was not set up for that..
I'd like to get the gmail back then I can look at the location where the tablet is get the police involved..
This women stole so much I just need the gmail back to stop her from scamming the next guy.