What was found
(APPROX 3.5 HRS INTO THIS FLIGHT) THE FLIGHT CREW "DETECTED STRONG CHEMICAL ODOR WHILE IN CRUISE, UNABLE TO DETERMINE ORIGIN, DIVERTED". THE FLT CREW DONNED 02 MASK AND DECLARED AN EMERGENCY WITH ENROUTE-ATC AND FOLLOWED PROCEDURES FOR A TPA DIVERSION. ONCE ON THE GROUND, CREW ADVISED MX OF OBSERVATION OF ODOR IN COCKPIT AND CABIN AREAS. TECHS WERE DISPATCHED TO PERFORM A/C INSPECTION, TSM 26-15-00-810-804 (ODORS IN THE CABIN AND NOT FIRE) & TSM 24-00-00-810-823 ( ELECTRICAL BURNING ODOR OR FUMES IN A/C). POST INTERIOR AND EXTERIOR INSPECTION REVEALED NO DEFECTS/ SOURCE COULD BE FOUND. ACFT WAS RETURNED TO SERVICE LATER ON.