THE ACFT WAS OBSERVED FLYING AT LOW ALTITUDE ALONG ABOUT A 5 MILE DISTANCE. SOME WITNESSES DESCRIBED THE ACFT ALTITUDE AS JUST ABOVE TREETOPS. WITNESS HEARD ENGINE SOUNDS AND SAW LIGHTS ON THE ACFT. THE ACFT FLIGHT WAS ON A SOUTHEAST DIRECTION BEFORE IT COLLIDED WITH RISING TERRAIN AT A HEIGHT OF ABOUT 1250 FT. THE WRECKAGE WAS SCATTERED ALONG A DISTANCE OF 375 FT AND ORIENTED ON A 160 DEGREE MAGNETIC HEADING. THE DESTINATION, PITTSBURGH, IS LOCATED SOUTHWEST OF THE DEPARTURE POINT, STATE COLLEGE. EVIDENCE OF ACFT MALFUNCTION WAS NOT DISCLOSED. THE ACFT HAD 1902 LBS OF CARGO INCLUDING 65 LBS OF DRY ICE WHICH WAS CONTAINED IN STYROFOAM BOXES. AUTOPSY AND TOXICOLOGICAL FINDINGS WERE NEGATIVE. THE PLT FLEW NIGHTLY, FROM STATE COLLEGE TO PITTSBURGH AND RETURNED THE FOLLOWING MORNING. HE OPERATED A BUSINESS DURING THE DAY. WITNESSES STATED THE PLT WAS WELL RESTED AND IN GOOD SPIRITS BEFORE THE FLIGHT.