The pilot was cleared to land on runway 25L at LAX with the first officer flying the approach manually. The crew of a commuter aircraft holding for departure witnessed the landing and the tail strike upon touchdown. According to information from the flight data recorder, the airspeed fell below Vref with a corresponding increase in the rate of descent. The attitude of the aircraft was 12 degrees nose high when the tail contacted the runway coincident with the main gear touchdown. The crew did not to use the appropriate checklist, nor arm the spoilers for the approach and landing.