As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 4878 DIVERTED DUE TO THE AFT BAGGAGE DOOR MASTER WARNING LIGHT ILLUMINATED. IN ADDITION, UPON DESCENT THE CREW HEARD A LOUD BANG AND DECLARED AN EMERGENCY. UPON LANDING, MAINTENANCE FOUND THE AFT BAGGAGE DOOR HANDLE IN THE FULL EXTENDED AND OPEN POSITION.