My sphere collider doesn't detect my player!

Hello and thank you for your time!

I have attached an empty child object to my zombie, an it is called PlayerSensor. It has a sphere collider into it, and it is inTrigger and radius 4. The idea is to switch to chase state in the finite state machine when this "playerSensor" detects our player.

However I am having trouble. Currently it doesn't detect the player and just detects the bullet but not when it enters into the 4m spheric perimeter but into the zombie's hit box itself.

Could you help me please?

Also as further reference I provide pictures:

"PlayerSensor"

http://imgur.com/V5eF3uh

Chase coroutine!

     IEnumerator Chase(){
         while (currentState == state.Chase) {
             towardsTarget = currentTarget.position - transform.position;
             MoveTowards (towardsTarget);
 
             if (towardsTarget.magnitude > maxChaseDistance)
                 ChangeState (state.Wander);
         
 
             yield return 0;
         }
     }

When event activates:

     void OnTriggerEnter(Collider other){
         Debug.Log (other.name+" detectado");
         if(other.CompareTag("Player")){
             Debug.Log ("PLAYEEER detectado");
             currentTarget=other.transform;
             ChangeState(state.Chase);
         }
     }

Debug log after testing:

http://imgur.com/evpftWm

Video tutorial I am following:

https://www.youtube.com/watch?v=3m4U_YgQtvQ&list=PLrvYYIXHycoogAkWSut5OTty_ujdNDV8u∈dex=18

THANK you for your time, I need some advice!