Marlowe, clearly not expecting to have fucked over Jones so severely, is kicking the wall in pain when he realizes who it is he just smashed into... hence he misses the creeper, and is nonetheless startled to the point of shock when the gun goes off in his face... the smell of cordite and blinding flash, the deafening ring-- and, for all he knows, a person just got shot in front of him.  "What the FUCK was that, man?!"  The now toppled body didn't look altogether wholesome... Marlowe stares, then as the door creeps open from the intruders behind him, he makes a connection; he's no murderer, but... these aren't normal people... are they..?  Maybe its the shock that lowers his moral bindings, but he has no qualms as he lifts the 10mm semi-auto, leveling it at the doorway, and squeezes the trigger on the first head through the door, sending its contents in a wet splash against the faux-wood panelling beside the door.  "Gotta go Jonesy... sorry for the door... which way?"