Police in the northern German city of Hamburg were searching the grounds of a secondary school for a youth armed with a gun who might have gained access to the premises on Tuesday. There are seven buildings on the campus, all of which are being searched, a police spokesperson said. In the meantime, the school has been locked down with students and teachers inside their classrooms. It was not clear whether the observed gunman had actually entered the building or just walked towards the school building and then possibly past the Otto Hahn School in Hamburg’s Wandsbek district. Police were called…