As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW - CREW REPORTED LEFT ENGINE THRUST REVERSER UNLOCK LIGHT ILLUMINATED IN FLIGHT. ACCOMPLISHED QRH PROCEDURE. EMERGENCY DECLARED RETURNED DFW LANDED WITHOUT INCIDENT. LIGHT REMAINED ILLUMINATED FOR DURATION OF FLIGHT AND AFTER AIRCRAFT REMAINED PARKED AT GATE. AIRCRAFT REMOVED FROM SERVICE. REPLACED LEFT THRUST REVERSER UNLOCK SWITCH. SYSTEM GROUND CHECK NORMAL OPERATION.