Police in Berlin are investigating a fire that affected a construction site and transformer substation in the Moabit district, amid heightened security concerns over a series of suspected sabotage attacks on Germany’s power grid. Authorities have not determined whether the fire was accidental or arson, and said the power supply was not affected. Separately, police in Wesel began major assessment operations after a security fence around another transformer substation was found cut open, Bild reported. German police were also searching for a man who sent letters claiming responsibility for last week’s attacks after apparent explosives were found at his home.