An investigation into last year’s deadly attack on a Christmas market in Berlin has revealed “gross mistakes” by German police and security services. The report commissioned by Berlin’s state senate says police missed several chances to arrest and deport Anis Amri, a Tunisian behind the attack. It says Amri – who was a known Islamist threat – could have been held on drugs charges before the 19 December attack. Presenting the report on Thursday, former prosecutor Bruno Jost said that “gross mistakes were made that should never have happened”. He said that although Berlin police had been earlier tipped that Amri was a potentially violent Islamist, surveillance was only carried on weekdays. Surveillance was dropped altogether after several weeks, with police believing that the 24-year-old Tunisian national was a small-time drug dealer.