As much as I despise the guy, one must concede that despite investigations by 2 hostile governments over the past 10 years, not enough evidence has been produced to satisfy even Pakistan's notoriously non-independent courts that Zardari is actually guilty of anything.
The greatest progress has been made by independent foreign courts in Switzerland. Pakistan's courts couldn't convinct Zardari despite 2 governments looking for evidence against him.
It was never about corruption, it's about power, NAB was just another way of breaking people, when they can't find some dirt on a politician they move on to calling them ghaddars (Javed Hashmi, Mengal et al are examples)