BERLIN — The shock of the rare burst of violence was multiplied by its odd circumstances: In a picturesque and normally placid little German city, three bodies lay in a hotel room, each one killed with a crossbow.

More than 300 miles away, another gruesome discovery made the case still more confounding. Searching the home of one of the three people who had died in the hotel, the police found two more bodies.

The German authorities are now trying to piece together a mystery that has attracted international attention for the unconventional weapon used and the lack of clear motive or motives behind five deaths in a country whose homicide rate is about one-fifth that of the United States.

“The use of crossbows as weapons is extremely rare,” said Walter Feiler, spokesman for prosecutors in Passau, adding that “they are rarely seen, except at medieval markets.”