The claim is made that Ahmadinejad stole the election, because the outcome was declared too soon after the polls closed for all the votes to have been counted. However, Mousavi declared his victory several hours before the polls closed. This is classic CIA destabilization designed to discredit a contrary outcome. It forces an early declaration of the vote. The longer the time interval between the preemptive declaration of victory and the release of the vote tally, the longer Mousavi has to create the impression that the authorities are using the time to fix the vote. It is amazing that people don’t see through this trick.
As for the grand ayatollah Montazeri’s charge that the election was stolen, he was the initial choice to succeed Khomeini, but lost out to the current Supreme Leader. He sees in the protests an opportunity to settle the score with Khamenei. Montazeri has the incentive to challenge the election whether or not he is being manipulated by the CIA, which has a successful history of manipulating disgruntled politicians.
There is a power struggle among the ayatollahs. Many are aligned against Ahmadinejad because he accuses them of corruption, thus playing to the Iranian countryside where Iranians believe the ayatollahs' lifestyles indicate an excess of power and money. In my opinion, Ahmadinejad's attack on the ayatollahs is opportunistic. However, it does make it odd for his American detractors to say he is a conservative reactionary lined up with the ayatollahs.
