D.C. Fire and Emergency Medical Services is investigating about a dozen fires set at night in trash depositories around Capitol Hill over the past month.Pete Piringer, D.C. Fire public information officer, said investigators believe an arsonist is setting fires behind the businesses on the 200, 300 and 400 blocks of Pennsylvania Avenue during evening hours. Piringer said there is a question about the number of fires, as some have gone unreported and some neighborhood listservs count the same fire multiple times — but they believe the fires are connected based on geography and time. D.C. Fire is working with both the D.C. Metropolitan Police Department and Capitol Police as the jurisdiction of each fire warrants in its investigation.A wave of small fires also hit Capitol Hill in late 2007. At least 16 fires were set, mostly in women’s restrooms in the Dirksen and Hart Senate office buildings. In that case, a Capitol Police officer pleaded guilty to charges related to the fires.Anyone with information about the recent fires should call 202-693-ARSON.