"It is awful to think that his life was lost in such a violent crime and (in such a) barbaric manner... I will never forgive," said Fay Berghaus, mother of Gregory Berghaus.
Fay Berghaus was giving evidence in aggravation of sentence for murderers Adam Roy Woest and Trevor Basil Theys.
They were convicted last week on nine counts of murder, one charge of attempted murder and one of armed robbery.
Berghaus told the court she had been "haunted" by the thought of the two men getting off on a technicality, or being granted some sort of amnesty.
She described her 43-year-old son, who had visited the Sizzlers gay massage parlour on that fateful day in January last year, as an integral part of a close family.
She described him as "kind and compassionate, (with an) incisive mind and wonderful sense of humour, who abhorred violence."
State advocate Anthony Stephen also called the surgeon who treated the massacre's sole survivor, Quinton Taylor, to testify.
Taylor survived being shot in the head twice and having his throat slit - the only one of 10 to survive the same treatment.
According to maxillo-facial surgeon Dr Sonil Aniruth, Taylor was "lucky" to survive.
Earlier, the Valkenberg psychiatrist who compiled a report into the Woest and Theys' mental fitness, said there was no reason to suggest taxi operator Theys had below-par intelligence.
No evidence of a violent past
Dr Larissa Panieri-Peter was being led by Nehemia Ballem for Theys during mitigation argument.
Asked about Theys' history of violence and possible homophobic tendencies, Panieri-Peter said there was no evidence of a violent past, and she was "unable to illicit any homophobic tendencies".
She said the only place Theys felt safe was in the court room after receiving death threats against himself and his family both in and out of the prison.
"He was upset, tearful and very anxious."
Attempts by Ballem to suggest that something in Theys had snapped during the killing spree, came to nought when presiding Judge Nathan Erasmus said there was nothing in the psychiatrist report to suggest that there was anything wrong with him.
"He was normal".
Tears welled up in Theys' eyes when his sister, who did not want to be identified for fear of victimisation, told the court her brother was a "helpful and loving person" who the children loved.
"My brother would never take a life... we are all still in shock," she said.
However, under cross examination by Stephen, she conceded that if someone committed crimes such as the Sizzler killings, they should pay because it was "not nice" to take someone's life.
The case continues.