Financial talk

there is someone who is making our lives hell. we bought a car from this guy which was all fine and above board, he then crashed his new car, had no insurance and so had no car or money as he had to pay for the other cars damages. he asked for the car back, we said no, we needed it, it was paid for, signed over etc all done and dusted. so someone has been pulling stupid stunuts like stealing aerial from our cars, window wipers etc. we are pretty sure its him, but cant prove it as its always done in the middle of the night. however this morning things went a step further. my partner left for work at 5am this morning and got to about 5 mins away then stopped as he felt something was wrong as the car was all over the road, he went out and checked. someone had loosened all the wheel nuts and the wheels were literally hanging on by a thread. he tightened them and went to work. he phoned me this morning and i checked my car as my daughter had an appointment this morning and the same ....was up with my car, the car i bought from him i fixed it and went to my appointment. i find it funny how its always our cars that get targeted and there is NOBODY else i can think that would do it. i know this isnt a newborn and baby question, but im always on this board and i know people give good answers here. is there anything legally i can do, as i know i dont have evidence to prove it was him also this person is on 21, and after buying the car and seeing his behaviour regarding it, i know he is quite immature. my boyfriend called the police this morning they said until we can prove its him they cant do anything. my BF said about a camera at our window, they said that couldnt be used as evidence as its invading his privacy by filming him without his knowledge. its all f****d up