FB.API callback issue

Hi guys, I'm trying to make a Facebook leaderboard in my game. So, when game starts , I log user in:

 if (!FB.IsLoggedIn)
             FB.Login("email,publish_actions,user_friends", LoginCallback);

Now, if logged, I make i request for scores:

  if (FB.IsLoggedIn)
         {
             OnLoggedIn();
         }

 void OnLoggedIn({
  FB.API("/app_id/scores", Facebook.HttpMethod.GET, ScoresCallback);
  }

Than, in ScoresCallback I create leaderboard in loop. But, in that loop I make a request for a profile pic of a user:

         for (int i = 0; i < data.Count;i++ )
         {
             leadscore = Instantiate(leadscore_prefab) as GameObject;
             leadscore.transform.SetParent(rank.transform.GetChild(0).GetChild(0));
             leadscore.GetComponent<RectTransform>().localScale = new Vector3(1, 1, 1);
             dataEl = data[i] as Dictionary<string, object>;
             user = dataEl["user"] as Dictionary<string, object>;
             name = user["name"] as string;
             id = user["id"] as string;
            
 
             leadscore.transform.GetChild(0).GetComponent<Text>().text = name;
            leadscore.transform.GetChild(1).GetComponent<Text>().text = dataEl["score"] + "";
            leadscore.transform.GetChild(3).GetComponent<Text>().text = i + 1 + "";
            FB.API("/" + id + "/picture", Facebook.HttpMethod.GET, LeadPicCallback);
 
         }
     void LeadPicCallback(FBResult result)
     {
         Sprite spr = Sprite.Create(result.Texture, new Rect(0, 0, result.Texture.width, result.Texture.height), new Vector2(0.5f, 0.5f));
         leadscore.transform.GetChild(2).GetChild(0).GetChild(0).GetComponent<Image>().sprite = spr;
 
     }

Now, my problem is, that LeadPicCallback is "too slow", the second iteration of 'for' loop goes before the first LeadPicCallback is completed, so it assigns the pictures wrong. What can I do with it, how can I delay loop iteration, and activate it when LeadPicCallback is completed? Hope you can help me guys ! ;)