Punched, kicked, insulted. That is the treatment at least four people received from security guards working on the Madrid subway lines in a shocking case of abuse of authority, which has triggered a criminal investigation...The assaults became public…after El Pais obtained video footage of the attacks apparently filmed by the guards themselves. Metro de Madrid - the company that operates the city's subway system - and the private security firms the company hire have admitted knowledge of the assaults…Three of…[the videos] involve guards of Prosegur, while one shows a person in a Casesa uniform, another private security company.