Order 66, as depicted in 2005's Star Wars: Revenge of the Sith, was a shocking betrayal, as Clone Troopers across the galaxy turned on the Jedi who, only moments earlier, were their comrades and leaders in the war against Separatist forces. The only act more treacherous was the attack on the Jedi Temple on Coruscant, led by Anakin Skywalker, that resulted in the slaughter of countless padawans and younglings. However, the clones played another role in that siege, detailed in a sequence cut from the film.
Released in unfinished form in 2010, and elaborated upon in the film's novelization (no longer considered canon), the scene shows the worst, and most painful betrayal, of the Clone Troopers as a detachment donned the robes of the Order to lay a trap for any Jedi who answered the false call to return home. This ploy feels even more sinister than the executions on the battlefields.
In the incomplete scene, Obi-Wan Kenobi and Yoda return to the Jedi Temple, where they're greeted by the imposters. Obi-Wan says, "You clones make terrible Jedi," before the clones fire their blasters at the two Jedi Masters. Of course, Yoda and Obi-Wan are faster and they easily strike down the clones.
The novelization provides additional details, revealing the fake Jedi are eight members of Decoy Squad Five, a detachment of the 501st Legion under Anakin Skywalker's leadership. However, in the prose sequence, Obi-Wan and Yoda deploy deception of their own: Obi-Wan pretends to be a homeless beggar with a Jedi youngling -- that is, Jedi -- seeking refuge in the temple. When the clones seek proof the child is a Jedi, Yoda leaps into action, saying, “My lightsaber, the first clue would be, hmm?”
Obi-Wan nevertheless seeks prevent any violence, but the clones pull their blasters anyway. "Six seconds later," the novel states, "all eight of them were dead."
The use of the Jedi robes in the ploy becomes more sinister and heartbreaking upon further reflection: The clones likely stripped robes from the bodies of Jedi they had murdered mere moments before this altercation. But even if the robes hadn't actually been removed from the dead, they still belonged to the very Jedi the clones had betrayed. Those robes are a symbol of their order and are supposed to symbolize peace, not deceit.
Order 66 nearly wiped out the Jedi entirely, and the few survivors of the Order not only have to live with that failure, but also with the knowledge that they were destroyed by those they trusted.