A gun scare at a German secondary school prompted an hours-long lockdown on Tuesday as police searched classrooms for a potential armed intruder.
It was feared that an armed man sighted in Hamburg might have entered the school buildings.
However, police said another possibility under investigation was that the young man had merely walked "in the direction of the school" before passing by.
The search by a special police unit ended with no unusual discoveries, meaning pupils were allowed to go home - although investigations were continuing site.
There were no reports of injuries or shots being fired.
The area around the Otto Hahn school was earlier sealed off in what was described as a major operation. Parents of children at the school were told to assemble in a nearby car park.
Germany has strict laws which require gun-holders to fulfil criteria on age and weapons expertise to obtain a firearms license.
But only last week, a student stormed into a university in the south-western city of Heidelberg and killed another student, then himself, with a gun he had bought in another country.
