Existence of common sense itself. The answer is generally pretty simple in situations like these. 'The sound came from the same direction, at least at the start.' The perpetrator was just one. A single attacker can change the direction of the bullet through a will.
A knight? Someone capable of this feat can only be a knight.
No, it can even be a mage, it should be a mage. Well whoever it was, they were after Darde's life and if he didn't do things properly, things might go bad. 'Nowhere is safe.'
If a person can shoot you out of your reach and break through all kinds of restrictions, then it can only mean one thing. "It's certain death." The small errors were just small, the shots still hit and from the movement and the closeness of the bullets each time they struck Darde, he knew the third one would do him in.