Answer: All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
As far as we (Iftaa` Department) know, Islamic banks state that they comply with Sharia in their various transactions, and a specialized Sharia committee makes sure that this is the case. Thus, this suffices to issue a Fatwa stating that it is permissible to open accounts at such banks and conduct investments with them. Accordingly, a Muslim isn`t required to verify that each transaction complies with Sharia unless it was found out that the bank fails to adhere to the rules of Sharia pertaining to methods of investment. If this is the case, then a Muslim person should investigate matters to be on the safe side as far as the teachings of Sharia are concerned.
In any case, making sure that Islamic banks abide by the rules of Sharia in their various transactions is the responsibility of the Sharia committees as well as the oversight bodies of these banks and not the Iftaa` Department. And Allah the Almighty knows best.