im worried if something will happen...?

ok, so to make a long story short. my son began to see a woman that lives in the buidling next to our house. he started to see her alot and always made it clear he was not looking for a relationsip and she always made it clear she wasnt either. well i guess they did have sex a couple times throughout the past 6 months we lived here but were just "friends". she eventually started to have feelings for him and for the past 4months has had a attitude due to my son having other female friends and spending time with them instead of her.

well the other night one of his female friends spent the nite at our house , the entire next day and at 2am when she went to leave two of her tires were slashed. prior to this the girl next door had seen the car in front of our house and called him asking whos car it was. he told her it was his friends and she began to ask if she could come over , he told her no. she began to start saying " why not ? we're just freinds right !" over and over again so he hung up on her. so its obvious she slashed the girls tires. what would any one else do in this situation ? i told them to call the police the nite it happened but she didnt.