What was found
AIRCRAFT WAS GOUNDED: DURING CLIMB OUT, AFT CARGO DOOR ECAM MESSAGED OPEN ON CLIMB OUT. RETURNED TO TO LAX, REACHED 9000 LEVEL OFF. EMERGENCY WAS DECLARED. FOUND STRIKER MISSING OFF AFT CARGO DOOR HANDLE. INSTALLED STRIKER AND INSPECTED ADJUSTMENT OF DOOR, IAW AMM 52-31-11.