Scoreboard teamkill."color" Is not registering entities

The scoreboard objective teamkill."color" is not incrementing when the player kills an entity, such as: Zombie, pig, villager ect.

I created an objective with the command:
/scoreboard objectives add fastpower teamkill.aqua fastpower
I then created a team:
/scoreboard teams add Speed Speed
Then I edited the options for team Speed:
/scoreboard teams option Speed color aqua

Next I spawn a mob, in this case a Zombie, at x=713,y=63,z=414
/summon Zombie 713 63 414
Then use the command (inside a command block)
/scoreboard teams join Speed @e[x=713,y=63,z=414,r=1]
This works, as does the next command.
/scoreboard players set @e[x=713,y=63,z=414,r=1,team=Speed] fastpower 2

But when I kill said entity my score does not increment, when I kill a player however it does increment. Any help or attention is appreciated as this problem, bug or not, wrecks a little game I was working on