(CNN) — The sign language interpreter widely ridiculed for his performance at the Nelson Mandela memorial stands by his work.
Thamsanqa Jantjie told CNN affiliate Radio 702 in Johannesburg that he is a fully qualified interpreter and has been trusted in the past with other big events.
"I've interpreted in many press conferences, including the presidential conference," he said. "There was no one at all that said I interpreted wrong."
Not so, says the head of the South Africa Translators' Institute.
There were complaints last year after Jantjie interpreted the proceedings at the ruling African National Conference elective conference, the institute's chairman Johan Blaauw told the South African Press Association.
"If I was not interpreting right, why was it was not picked up at that time?" Jantjie said. "You must remember, you are talking about an interpreter who has been interpreting through these years. And if I was interpreting wrong through these years, why should it become an issue now? It's one of the questions I've never ever gotten an answer for."
The radio station interviewer asked Jantjie to comment on media reports that he was hearing voices in his head and hallucinating during the Mandela event Tuesday.
Pressed twice, Jantjie reluctantly acknowledged that he was a "patient receiving a treatment in schizophrenia."
As outrage over his interpretation skills grew, so did questions over who hired him.
A spokesman for the ANC said the party had not hired him for the Mandela event.
"We have used him on some occasions. But yesterday was not an ANC event. So we cannot answer for yesterday," spokesman Jackson Mthembu said Wednesday.
The South African government was investigating the reports, said Collins Charbane, minister for performance monitoring and evaluation in the presidency.
Jantjie told Talk Radio 702 that he was hired by a company called SA Interpreters, which was hired by the ANC. He also said he's formally qualified as an interpreter and that his qualifications are filed with the company.
"I think that I've been a champion of sign language," he said.
The national director of the Deaf Federation of South Africa sees it differently. He called Jantjie a "fake interpreter."
"The deaf community is in outrage," said Bruno Druchen. "He is not known by the Deaf Community in South Africa nor by the South African Sign Language interpreters working in the field."
The man showed no facial expressions, which are key in South African sign language, and his hand signals were meaningless, Druchen said. "It is a total mockery of the language," he added.
The service to commemorate Mandela, who died last week at 95, was broadcast to millions of viewers.
While dignitaries addressed the crowd at Johannesburg's FNB stadium, Jantjie produced a series of hand signals that experts said meant nothing.
"It was almost like he was doing baseball signs," deaf actress Marlee Matlin told CNN on Wednesday, through a sign-language interpreter. "I was appalled."
Though each country has its own sign language, all of them entail facial expressions, she said. She called his lack of facial expression "a giveaway."
"I knew exactly right then and there that he wasn't authentic at all, and it was offensive; it was offensive to me."