At 1153 Eastern time, the airplane was substantially damaged when it impacted the Penobscot River. The solo commercial pilot was killed. Instrument conditions prevailed; an IFR flight plan was filed. The operator intended to ultimately deliver the airplane to a customer in Russia and additional fuel tanks were installed for the planned flight across the Atlantic Ocean. Shortly after departing and while in cruise flight at 5000 feet msl, the pilot was cleared to maintain 6000 feet. However, the airplane began to descend. Soon thereafter, ATC instructed the pilot to maintain at least 3000 feet. The pilot replied that he was trying, and ATC subsequently provided the pilot with a vector to divert to a nearby airport. No further transmissions were received from the accident airplane. Airmet Zulu was in effect at the time of the accident and advised of moderate ice below 13,000 feet. The Airmet forecast the freezing level ranging between the surface and 2500 feet.