Only front panel comes off when opening, instead of entire screen?

Some time ago my phone died, and because it is quite old, I think the battery is at the and of it's life cycle. I tried opening the phone to take a look at the battery. Following the instructions on this site, I removed the two screws at the bottom and used a suction cub to lift the screen. But instead of the entire screen, only the front glass comes off.

It should open like this:

http://i921.photobucket.com/albums/ad53/...

But mine opens like this:

http://i921.photobucket.com/albums/ad53/...

I tried using glue to keep it together, but the glue wasn't strong enough. I also tried using an adhesive sticker (http://www.gultek.eu/images/P/iPhone%203...), but it isn't strong enough either (maybe the glue remains keep the sticker from sticking properly).

Is there any other way to get to the battery?

Thanks a lot in advance!