Do the people who were doing the robbing know you took the video? If not how would they know who they would need to take revenge on? Just send the video anonymously to the police. If they do know you took it then tell the cops you have it and you will give it over with a warrant. Then the robbers will think you didn't have a choice. If they get caught and it goes to trial they will see the video. They do not have to know it came from you
