As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURN TO BDL. SMOKE IN REAR OF CABIN. AFT SMOKE DET SOUNDING, SMOKE CLEARED CABIN PRIOR TO LANDING. FOUND APU LEAKING OIL INTERNALLY. PERFORMED DUCT AND PACK BURN OUT PROCEDURES. REPLACED LEFT AND RIGHT COALESCER BAGS. RAN BOTH ENGINES TO TAKEOFF POWER, WITH BOTH PACKS ON. NO SMOKE NOTED. INSPECTED ALL PNEUMATIC DUCTS, NO CONTAMINATION FOUND.