Issues with criminal neighbour

Looking for advice as to what to do with my neighbours.

Living directly next door to myself is a father and son. The father is a relatively nice man who says hello, asks how things are and works a normal job. The son on the other hand is genuinely one of the worst human beings I have ever encountered. The father is well aware of what his son is and has on occasion covered for him and helped him avoid situations involving the police.

I have never directly engaged with him but the house that we live in has paper thin walls and I hear him daily saying the most appalling stuff. He screams how he’s going to smash his partners head in, how he’s going to have people killed, how he going to have someone’s house burnt down. He explodes about once every week or so over the phone and I hear every thing that he’s done or is planning to do.
I feel that most of his comments are just bravado and he wouldn’t actually have someone killed but he is at least a mid to low level criminal.

Until now, I have minded my own business and tried to just ignore it as best I could but recently their house has been targeted and I feel that I have to do something. Over the past couple months their house has had their cars smashed up, the front door has been broken down and the most terrifying incident involved a stolen car being rammed into their car in the driveway resulting in it hitting the front of the house. Each attack seems to be escalating which is the root of my concern.

I’ve spoken to the police for advice anonymously and they said there pretty much nothing that can do unless I give a detailed statement which for obvious reasons I’m reluctant to do.

I’m thinking that maybe I could speak to the father and telling him that I’ve had enough and I’m worried about my personal safety and fire bomb attacks on homes in my area aren’t the most uncommon event.

Any thoughts on how I should proceed?