Clue: One cause of MD being fired may be used in part of 9 18 23 down, 27 1 across (6)
Answer: WEAPON
Explanation: Definition: may be used in part of 9 18 23 down, 27 1 across
The clues referred to give (n)AGAT HA(uled in) CHRISTIE MURDER, but I can't work out the wordplay. *See comment 2 below for a possible explanation.