Service Brakes Problems of BMW 318

My vehicle was parked on a slight hill and the hand brake was pulled up to its full capacity. My brother sat in the car and smoked a cigarette before going to his appointment. After he returned from his appointment, the vehicle could not be found. After looking around, he realized that the vehicle had rolled down the hill, across a busy two-way main road in the downtown area of the city and hit the wall of the at&t building. Thank god no pedestrian was walking during this time and no car was passing by. My insurance paid $12,000 in damages to the building owner and the damages to the car was massive. My premium increased due to this incident because at the time, BMW stated that there were no recalls on the hand brake. The vehicle was in tip top shape and the only issue I have ever had with it was having to get the hand brake adjusted periodically because it kept slipping causing the vehicle to roll even while extended.