Nuon Chea, Pol Pot’s former lieutenant, told the court that Norodom Sihanouk had visited members of the Khmer Rouge for a week in 1973.
Thousands of pagodas were destroyed, along with the banking and education systems, after the regime came to power in 1975.
When the Khmer Rouge took over Phnom Penh, on April 17, 1975, they began marching people out of the city almost immediately.
Ieng Thirith would then be re-evaluated within six months to determine whether she is fit to stand trial, the court said.
As the court undertakes its second trial, judges have said sexual violence will not be counted among the crimes in Case 002.
Many people joined the movement in an effort to put the monarch back on the throne.
In recent testimony, Nuon Chea accused the Vietnamese of their own atrocity crimes, a claim Vietnamese officials deny.
Monday's session was dominated by the Khmer Rouge's chief ideologue, Nuon Chea, the man known as Brother Number 2.
The two cases have fueled concern among court observers they are being stymied by government interference, a charge that officials deny.
It took the prosecution one and a half days to put its argument against the Khmer Rouge leaders to the court.
In the past, Nuon Chea and Ieng Sary’s defense officials have requested the former king be summoned, to no avail.
The court will now move on toward the hearings of evidence, beginning Dec. 5.