Kenyan cult leader Paul Mackenzie and 29 associates were charged on Tuesday (February 6) with the murders of 191 children.
Their bodies were among more than double that number unearthed in the Shakahola forest last year.
Prosecutors allege Mackenzie ordered his followers, who lived in several secluded settlements within the forest, to starve themselves and their children to death so they could go to heaven before the end of the world.
It is one of the world's worst ever cult-related disasters.
At a court in the coastal town Malindi, the defendants denied all the charges.
One suspect was found mentally unfit to stand trial.
Mackenzie was arrested last April and has already been charged with terrorism-related crimes, manslaughter and torture.
According to some of his followers, the former taxi driver forbade members of the Goods News International Church from sending their children to school or going to hospitals when they were ill - labeling such institutions "Satanic".
Mackenzie's lawyer has said he is cooperating with the investigation into the more than 400 deaths.
The judge said the 30 defendants are due back in court for a bond hearing on March 7.