Rotate bone so child points at target

OK, here’s my problem. I have an enemy in my game which needs to be able to aim at the player. Up to this point, I’ve simply rotated the gun, but, now I want to add additional functions/animations to allow the enemy to do things like playing melee animations. To this end, I want to rotate the enemy’s torso around it’s y axes (so, vertically) so that the enemy can aim at the player.

The problem is, I need the gun, which is a child of the torso, to point at the player. Any ideas/hints on how would I go about doing this?

Locomotive system, I believe unity has an example project on this and there are some pretty detailed posts here on the forum.