While a passenger on a ship en route to Astra, Bennett murdered a fellow passenger and was caught. When the ship crashed on Dido, Bennett killed the rest of the passengers and the natives to cover up his earlier murder.
Vicki, who hadn't attended the meeting between the humans and natives, was unaware that Bennett had killed anybody, and he planned to use her innocence to protect himself from the authorities. He told her that the natives had wiped out the others, and pretended that he had been paralysed in the attack.
He also claimed that he was protecting them from a native named Koquillion, who was actually Bennett in a ceremonial mask used by the natives. Bennett's crimes were exposed by the Doctor, whom he attempted to kill. Before he could do so, he was confronted by two surviving natives, and while backing away from them, fell from a rock ledge to his death.
Years later, the Doctor hallucinated about Koquillion when the Keller Machine turned his worst fears against him.