The trial, which is set down for 15 days, started on October 28 in the Gauteng High Court in Johannesburg. The inmates are being represented by Lawyers for Human Rights (LHR).
Van Zyl was testifying on Monday about medical examinations which she conducted on August 15, 2014, five days after the alleged assault and torture.
She said she completed a J88 form – a form generated by the Department of Justice which serves as medical evidence – in which she recorded everything she observed and made conclusions based on the patients' history of what happened to them, and her clinical examination.
She testified that some of the injuries on the inmates were classified as severe. She tested the severity of the injuries by touching the patients to identify any bruising and testing their range of movement, she said. She also looked at the size of the bruising.
Xolani Zulu had three severe injuries: one on his upper left leg, lower left leg, and right hand, according to Van Zyl. She demonstrated to the court how she tested another inmate, Abel Mpasha, who had an arm injury prior to the alleged assault.
Mpasha, who was wearing a sling around his arm, told Van Zyl that he had injured himself during a soccer match.
But when she looked at his injury, she said she saw fresh bruising and swelling around the elbow that was not consistent with an old injury.
She demonstrated that Mpasha experienced visible pain when he moved his arm past a 40 degree angle. She said that should not have been the case considering the time that had passed since his soccer injury.
Dispute over severity of injuries
Under cross-examinition, advocate Luyanda Mtukushe, for the DCS, said Van Zyl's opinion on the severity of the injuries was questionable.
He said she had not noted the severity of the injuries on her J88 and notes, which, according to him, she should have done.
"Any reasonable medical practitioner cannot just walk away without recording severe injuries [on the J88 forms and on the notes]," said Mtukushe.
He also said Van Zyl did not use any medical equipment to measure the size of the bruises, so her observation could have been inaccurate.
He said medical practitioners usually used scales to grade the severity of injuries, but that Van Zyl had not used this "objective measure". He argued that there was no way for other medical practitioners to confirm her findings using an objective measurement.
"You want this court to believe that you omit to use a system that doctors would rely on in grading injuries… and your opinion is not speculative, to the extent that it refers to the severity of the injury," he said.
But Van Zyl said equipment was not allowed into the prison, so she had used her knowledge and experience to measure the size of the bruises.
She referred to the oath signed at the beginning of each J88 form which held her liable for prosecution if she lied.
The trial continues.