Imagine. There's a blast outside Indira gandhi Intl Airport, New Delhi. One of those arrested has a SIM card belonging to an Australian.
The first thing Australia would do is get their citizen to safety by packing him off to Australia and then say that Indian Police is making absesless charges.
And of course, our Govt. will just sit and watch, while a CBI team will go and come back empty handed, without even being allowed to meet the Aussie suspect.