Fading in thumbnails as they load

Hi, I know I’ve seen a tutorial for this before, but I just cant seem to find it. I have many thumbnails being placed into a container and I would like each thumbnail to fade in as it is placed.

Should I be using an Event.COMPLETE listener and then tween the alpha of currentTarget or something?

I assume the code would go in/around here:

function thumbLoaded(e:Event):void{
var my_thumb:Loader = Loader(e.target.loader);
container_mc.addChild(my_thumb);
}

Any suggestions?