The highest court in the Netherlands has ruled that its police force is liable for damages suffered by victims of a deadly shooting in a shopping mall. It comes after police granted a weapons permit to the shooter despite him having a history of mental illness. On Friday the Supreme Court up held a ruling from the country's lower that the police were wrong to issue a gun license to Tristan van der Vlis because he was known to have psychological problems. Van der Vlis shot and killed six people and injured 17 more at a shopping center in Alphen aan den Rijn on April 9, 2011, before killing himself. In a statement the police said that the ruling "has possible consequences for how police will handle applications for weapons permits in the future". Since the incident people applying to own a gun must undergo psychological testing and provide three references.<br/> The number of legal weapons in the Netherlands fell to 197,357 last year – the lowest total in 12 years.