Quick question about my script

I’m doing a photo slideshow and I have 4 photos. I have them displaying randomly with TweenLite, however I have 2 more things I’d like to do with it but I really don’t know how to do them. I’d like for the photos to display randomly forever, as if the script would never end. Also, I’m curious as to why only 3 of the 4 photos are displayed when I run the swf.

Here is my script thus far:

import gs.TweenLite;
import gs.easing.*;

var photoNums:Array = new Array(photo_1,photo_2,photo_3,photo_4);

var randPhotos:Array;

var currentPhoto:uint = 0;

function shuffle(a:Array):Array 
    var len:Number = a.length-1;
    for (var ivar:Number = len; ivar>=0; ivar--) 
        var p:Number = Math.floor(Math.random()*(ivar+1));
        var t = a[ivar];
        a[ivar] = a[p];
        a[p] = t;
    return a;

randPhotos = shuffle(photoNums);

var timer:Timer =  new Timer(5000);
timer.addEventListener(TimerEvent.TIMER, onTimer);

function onTimer(evt:TimerEvent):void 
    if (currentPhoto > 0) 
        TweenLite.to(this.randPhotos[currentPhoto], .75, {x:140, y:0, alpha:0, ease:Back.easeInOut});
    TweenLite.to(this.randPhotos[currentPhoto+1], .75, {x:600, y:0, alpha:1, ease:Back.easeInOut});

    currentPhoto += 1;

Any help would be extremely appreciated.