The former head of the Khmer Rouge’s Tuol Sleng prison objected to testimony of an alleged survivor Tuesday, telling the UN-backed tribunal the man’s claims he was held and then released were not possible in the deadly facility.

Lay Chan, 55, told the court he had been held for three months at Tuol Sleng, which, under the administration of Duch, or Kaing Kek Iev, saw the deaths of nearly all its inmates.

Lay Chan said he was arrested outside of Phnom Penh and taken to Tuol Sleng, known to the Khmer Rouge as S-21, for torture and interrogation. He was accused of stealing rice for “the enemy,” betraying the regime and being an agent of the CIA, he said.

“When the interrogator questioned me, I was blindfolded, handcuffed and shackled,” he said. “The interrogator beat me until I was unconscious during the interrogation.”

Lay Chan said he was held for three months, and then released. If so, he would be a potentially unique case. All but a handful of people were killed after interrogations—prosecutors say 12,380 people met their deaths after Tuol Sleng.

Those who did survive managed were alive at the prison when it was liberated by Vietnamese forces as they drove the Khmer Rouge from Phnom Penh, in January 1979.

Duch, who is charged with crimes against humanity, war crimes, torture and murder for his role as the prison’s administrator, told judges he sympathized with Lay Chan, but he found his testimony unbelievable.

“All inmates at S-21 found it difficult to avoid being murdered,” he said. “He said he was sent to S-21. He was released from S-21. It is not possible. I would not have dared to release him. All the inmates that I received at S-21 were sent by the [Khmer Rouge] Permanent Committee.”

“People coming into S-21 were killed,” Duch said. “I have read the list of names of inmates at S-21. I did not find the name of Lay Chan. I recognize that Lay Chan had suffering, but I stress there is no evidence to confirm Lay Chan was tortured at S-21.”

A civil party lawyer told judges there was no documentation related to Lay Chan’s alleged incarceration.