Forum Post: Police as Wall st security guards

Why do wall st business get to use the NYC police department as there own private security. Some Police there as witness as and a buffer I understand but shouldn't Wall st be paying for there own security??? What next , using city sanitation workers to clean there buildings. Firemen to wash there cars. I thought the police are paid to arrest criminals?? Protesting isn't criminal so why are there so many of them there. I hope the wall st business pay for this security out of there own pocket.