Squatter living in Vacant Home on 3151 Elston Drive San Bruno CA

We have some stranger Squatter living in the abandoned house next door to me at 3651 Elston Drive. He sneaks in and out of this property late at night so he will not be detected. The police have talked to him before but he keeps coming back into the house. This man is has talked to the neighbor across the street from 6351 Elston Drive and told him that he is trying to take possecion of this property through *Adverse Possession* as neighbors we do not know if this man is dangerous or what he isactually doing in that property the police will not help us what can we do as neighbors for all of us to feel safe in out own community???