Time Magazine reported two days ago that the Western Spy agencies say the Iranian story about catching the assassin networks are reliable. The timing of the Time story, just as Ben Zygier was hitting the headlines strikes me as something which could be more than a coincidence.
Having said that, Zygier was arrested in 2010 and the last Israeli assassination was in January 2012. The Iranians claimed to have wrapped up the network in June 2012.
The Iranians aren't the only ones to have wrapped up some Israeli networks in recent years. Hezbollah has also had some successes, though reports I read suggested they did it by tracking rarely used cell phones.
Ha'aretz suggests this morning that Zygier talked too much and the Australian spy services got onto him. Someone in the Aussie service may have leaked information to the Iranians and Zygier might have damaged Israel indirectly. As long as we don't know what he was accused of, its hard to judge what damage he did and how justified his treatment may or may not have been.