Police in Berlin are investigating after 12 people were injured when the roof of a party boat collapsed in the German capital’s central Mitte district. Around 120 people were celebrating on the boat late on Tuesday when the accident occurred, Berlin police said on Wednesday. The cause of the accident is under investigation, police said. A witness told the Bild tabloid that partygoers had been sitting on the roof shortly before it collapsed. “It was a concert on a boat, but you could also sit on the roof,” the witness said. In total, nine women and three men between the ages of 22 and 31 years …