At about 12:20 EST, the pilot of a Cessna 414A was killed when the airplane crashed into water -mile offshore. The flight was en route from Hyannis, Mass., to New Bedford, Mass., when the pilot reported that hed lost the artificial horizon and was in IMC. At 12:19:18, the controller issued the pilot a low altitude alert, which the pilot acknowledged. A witness about 1 mile north of the accident site stated he heard the sound of engine noise coming from the water and thought it was a power boat. He described the sound as loud and constant. The sound lasted for about 30 seconds and was followed by an explosive collision/impact sound, then all was quiet. A Coast Guard searcher said that visibility at the accident site was approximately one-eighth of a mile in fog.