"There was zero percent accuracy. He couldn't even get the basics right. He couldn't even say thank you.
"You're supposed to indicate with your facial expressions, even if it's not an exact sign. He didn't indicate that (booing of Jacob Zuma) at all. It just passed him by.
"Nobody knows who he is. Even at this hour we still don't have his name."
Paul Breckell, chief executive of Action on Hearing Loss, said: "The use of appropriately qualified communication support is crucial to ensure that deaf people can engage with and access the same opportunities as hearing people.
"Sign Language, be it British, International or South African, is a visual and expressive language yet the limited number of signs, the amount of repetition, lack of facial expressions and huge gaps in translation meant that deaf or hard of hearing people across the world were completely excluded from one of the biggest events in recent history."
The memorial was also affected by faulty public transport which prevented some mourners from getting to the event and a faulty audio system that prevented some of the crowd from hearing leaders' speeches.
A man being criticized by sign language experts for providing fake interpretations while standing close to President Obama and other heads of state at Nelson Mandela’s memorial says he becomes violent “a lot” and was hallucinating during the event.
Thamsanqa Jantjie did not describe his qualifications for being a sign language interpreter, but told The Star he works for an interpreting company that paid him $85 for working Tuesday's event, according to The Associated Press. He told Radio 702 on Thursday he's receiving treatment for schizophrenia and had an episode while on stage at FNB Stadium in Johannesburg.