TORTURE at Tuol Sleng prison largely took the form of beatings and electrocution, but also included medical experiments and a failed attempt at waterboarding, prison chief Kaing Guek Eav, alias Duch, told Cambodia's war crimes court Tuesday.

"First, live prisoners were used for surgical study and training; second, blood drawing was also done," Duch said in his first public admission of the practice.

He also detailed how interrogators fell into three groups: the "cold" group, which did not apply torture; the "hot" group, which "would beat the prisoners immediately if the confessions were not extracted as they wanted"; and the "chewing" group, which subjected prisoners to long-term torture.

Duch spoke calmly for much of the day's questioning, though he became visibly upset when discussing detainees whom he had previously known.

These included former Northern Zone Secretary Koy Thuon, alias Khuon, and Phung Ton, an international law professor who died at Tuol Sleng and whose wife and daughter were in the public gallery.  

Duch described devising torture methods in conjunction with superiors, recalling how they "agreed that beating would be the general method for torturing", as well as how they tried to employ a version of waterboarding in which water was poured down a detainee's nose, a method he said had been used by security forces working under then-prince Norodom Sihanouk and Lon Nol.

Duch said this technique was only attempted once and abandoned when the water "could not get through [the victim's] nostrils".

He  said he did not believe the information contained in the confessions, saying, "Pol Pot at one point did not even believe that the confessions were of true information." Duch acknowledged performing a handful of interrogations, though he dismissed reports cited by Nil Nonn that he personally kicked and beat prisoners.

ADDITIONAL REPORTING BY AFP