The incident occurred at 12.45 pm local time (1145 GMT) close to a building in the town of Rot am See in the federal state of Baden-Wuerttemberg.
Police in the nearby town of Aalen said the incident appeared to be linked to a "personal relationship", adding there was no indication that there were additional perpetrators.
Rot am See is located some 135 km (84 miles) southeast of Frankfurt, close to the medieval town of Rothenburg ob der Tauber