Why did he lie to the police?
So, the boyfriend character goes to the highschool after the fire thinking his girlfriend might be there. The police found no trace of her except her purse. The bald investigator becomes suspicious of the young man and takes him to the girlfriend's house to look for her, as they enter the empty house, she calls home.
Phew!This means she's alive and that the cop will leave the boyfriend alone as there isn't a missing or potentially dead person anymore.
Yet somehow, the boyfriend starts pretending he's talking to someone else on the phone to trick the investigator....WTF? What did he hope to accomplish by doing that?