Many law firms do not handle these types of cases for the difficulty in handling them. (It's not easy to sue the police). My advice for you would be to contact the bar association in New Jersey and ask for a recommendation to a police brutality/civil rights law firm. They should be able to point you in the right directioin. Here is there contact info: http://www.njsba.com/
Also, as the above commenter said, most firms will take these cases on a contingency basis--meaning they will take care of the up-front costs of the case and will not charge you money unless they are successful.
This should not be construed as legal advice or the making of an attorney-client relationship. this information is purely for informational purposes and should be treated as such.