It's well know by know that those who did the most incitement, like Avishai Raviv with his group Eyal, was in fact agent/provocators of Shabak. It's likely the the murder itself as well was staged as an attempted murder by Shabak in order to blacken the right and especially the "settlers". Somthing might have gone wrong, and Rabbin was murder in real.
Firebomb thrown during demonstration in northern Israeli town of Umm al Fahm (Haaretz)
from the article: Rabin's murderers are still free and happy