As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STL - INFLIGHT ORD-DFW. CREW REPORTED 2 AFT LAVATORY SMOKE DETECTORS ALARMED THEN SMOKE DEVELOPED ON THE CABIN NEAR ROWS 9 TO 14. EMERGENCY DECLARED FLIGHT DIVERTED STL LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND OIL IN AUXILIARY POWER UNIT BLEED AIR DUCT. REPLACED AUXILIARY POWER UNIT. SYSTEM GROUND CHECK NORMAL OPERATION.