As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE AIRCRAFT WAS GROUNDED. WHILE IN CRUISE CREW O2 PSI DROPPED TO ZERO AT FL 330. THE FLIGHT DECLARED AN EMERGENCY, DIVERTED TO ELP, LANDED OVERWEIGHT AND WITHOUT FURTHER INCIDENT. DESCENT RATE NORMAL. ROLL OUT AND TAXI IN NORMAL. REPLACED OXYGEN BOTTLE (CYLINDER) PER AMM 35-11-41. ALL CHECKS GOOD. INSPECTION SHOWS OBSERVERS MASK TO HAVE BEEN LEFT ON.