Referencing variable symbol

I am using Starling with AS3. I have set up a texture like this:

var tilea:Texture = Texture.fromBitmap(new lettera());

There are a series of these textures.

In order to display the textures I use this:
var suffix = “a”;
thisTile = “tile” + suffix;
var tile1:Image = new Image(thisTile);

but this does not work,
the error it gives is: Type Coercion failed: cannot convert “tilea” to starling.textures.Texture.

what is the best way for me to reference the tilea texture in this manner?