BitmapData transparent

I’m interested in loading a Bitmap from a URL, and setting some pixels to become transparent. I think there’s a problem with the definition of the loaded bitmap since it’s ‘transparent’ property is automatically set on “false” when loaded.
I didn’t manage finding a manner to switch the property of the loaded Bitmap to “true” so the 32bit color can take affect with the 2 first bytes defining the alpha values.

I don’t know how to solve this issue, and i’ll be grateful for any suggestions.

Regards,
Oml