During the Clone Wars, a battle took place on the planet Phorose.
When the Separatists invaded Phorose, the Jedi Order sent Jedi Master Plo Koon and Padawans Ahsoka Tano and Barriss Offee to lead the defense of the planet.
During the battle, the Padawans were ambushed by droid tri-fighters and fell in an underground temple, leading to the accidental discovery of a community of Ru. However, a group of battle droids ambushed the two Jedi and destroyed the Ru temple. After the temple's destruction, Tano and Offee decided to evacuate the remaining Ru to a safe location, far from the battle. Unfortunately, the LAAT/i gunship carrying the two Padawans and the Ru was ambushed by Vulture droids, leading to the death of the Ru, with only two Ru and the two Jedi surviving.
The battle ended with the Galactic Republic's victory, however at a great cost, as most of the Phorosian capital was destroyed in the battle and the majority of the Ru were killed.
After witnessing the death of these innocents, Offee started to question the ideals and motives of the Jedi, believing that the Republic and the Jedi Order were culpable for their deaths. In time, she reached the conclusion that the Jedi Order had become an instrument of the dark side, by becoming generals in a war to protect a corrupt Galactic Senate. This encouraged Offee to help in a terrorist act against the Jedi Order and blame it on Tano, her closest friend.