@Pinkglitter I didn't knew that police case is involved , and your father had died . May his soul rest in peace . Yes then you should get it opened through apple service , or repair centre , but only after permission from cops or lawyer .
@Pinkglitter in that case you might want to try using his phone number and email. Apple is very strict regarding Apple ID stuff. I have been locked out of my Apple account on my new iPhone and I still have access to email and phone numbers