He catches up with the assassin rather quickly, the dwarf's stumpy legs, even magically enhanced, no match for the Summer Knight's speed. He doesn't even look behind him, not slowing down in his mad dash to reach the exit, before anyone can organize a defense. It's hard to tell any details about him, as he's dressed in all black, and carrying a heavy crossbow, but given the circumstances, there's little doubt that he's the murderer.