Hey,
could you provide some more information?
Shall the AI always focusing you?
Assuming He watches and looks with his head.
How do you define the 90, -90? Do you have any Field of Vision for the AI? If yes,
why not telling it when the Player Location isnt inside this field disable focus → return to look like a normal guy → move backward (maybe reverse the walk animation) → Check if the Player is in fieldrange again, set focus back.
if not or If i got you wrong, please tell me what and when your AI should do something 
kind regards