On 15 September 1981, 10-year-old Ursula Herrmann headed home by bike from her cousin’s house. She never arrived. So began one of Germany’s most notorious postwar criminal cases, which remains contentious to this day

In the Alpine foothills in the far south of Germany is a vast lake called the Ammersee. Its shores are dotted with centuries-old villages where wealthy families from Munich buy large second homes and tourists drink beer at waterfront restaurants. At the north end of the lake is a pair of such villages, Eching am Ammersee and Schondorf, less than two miles apart. Separating them is a block of spruce forest that attracts hunters, joggers, mountain bikers and in the late summer 38 years ago, kidnappers preparing to commit what would become one of the country’s most notorious postwar crimes.

After class on Tuesday 15 September 1981, the first day of the new school year, a 10-year-old girl named Ursula Herrmann returned to her house in Eching. Ursula, the youngest of four siblings, practised piano with her oldest brother Michael, and then headed off to her late afternoon gymnastics lesson in Schondorf, cycling through the forest along the lakeside path. When the gym class was over, she went to her cousin’s house in Schondorf, where she ate dinner. At 7.20pm, Ursula’s mother phoned the aunt to say her daughter needed to come home. The shadows were lengthening but it was still light, and the cycle ride would only take 10 minutes.