How can i destroy a gameobject?

update:

I was told everything is working ok but because the zombie in animated it works different from the other 2 and afte I attached the script to the parent of the head it did in fact work destroy the entire zombie (which i don't want)

It was recommended i swap to set active so ive changed it from destroy to SetActive

 void OnTriggerEnter (Collider col) 
 {
     if (col.gameObject.tag == "Bullet")

     {
         Debug.Log ("Good shot!");
         gameObject.SetActive (false); 

This but this deactivates box collider (set to trigger) but not head - any suggestions?