Ext WDSmartware WD500AADS case opening?

[TechTard]

I have an Ext. WDSmartware WD500AADS and i would like to open the case to get to the internal drive but i dont see anyway of opening the metal case after i took off the plastic casing. Ive serched all over the web and i cant find how to open this particular model.
If anyone can help please do.
thnx in advance.