Who gets the Boss Crate in Zombie Mode?

Hi,
i've got to the last round in Zombie Mode Easy for several times now. Each time, I stood right in front of the bosses and unloaded my mag right into their head (since I use Thompson and RPK in ZM, I have quite large mags), even if that meant getting killed. I usually still had 2 spare lives when reaching Wave 20, so I could afford to go down to 0 spare lives. Hovewer, I haven't got a boss crate yet, not even a single time, although I got a "Headshot" kill mark one time, when the boss died. So my question is: Who gets the Boss crate? The one who delivered the final shot that destroyed the boss? The one who did the most damage to the boss? Or simply a random player who was still alive at the end of the game?