Judges at the Khmer Rouge tribunal in Cambodia have ruled that a former prison chief, known as Comrade Duch, should not face additional charges.
He already faces charges of crimes against humanity, but prosecutors wanted to add conspiracy charges too.
They argued this would make it easier to prosecute other Khmer Rouge leaders.
The BBC reports the ruling means the final obstacle to starting the trials has been lifted.
Prosecutors earlier said the scope of the indictment was not wide enough.
Specifically, they wanted him to stand accused of being part of a joint criminal enterprise with other Khmer Rouge leaders - a conspiracy to murder, starve and torture Cambodians in the late 1970s.
Judges rejected this, but they did widen the scope of the charges to include torture and pre-meditated murder.
As many as two million people are thought to have died under the Khmer Rouge.
