By Alexander Smith, NBC News contributor

The vetting of a sign language interpreter who got within three feet of world leaders including President Barack Obama during Nelson Mandela's memorial was being investigated Thursday after organizers admitted they were unaware of his violent history of schizophrenic episodes.

Thamsanqa Jantjie, 34, was accused of gesticulating gibberish during Tuesday's service. Members of the deaf community said his movements did not resemble any recognized form of sign language and some groups accused him of being a "fake."

Jantjie told Johannesburg's Star newspaper he started hearing voices in his head and hallucinated while at the Mandela event, resulting in gestures that made no sense and outraged deaf people around the world.

The South African government on Thursday admitted that "a mistake was made."

Jantjie said he was happy with his performance -- describing himself in an interview with Talk Radio 702  as a "champion of sign language" -- but added that he may have suffered a schizophrenic episode while on stage.

"There was nothing I could do," he told the Star newspaper. "I was alone in a very dangerous situation. I tried to control myself and not show the world what was going on. I am very sorry. It's the situation I found myself in."

Jantjie later told The Associated Press that during the memorial he saw "angels" and had been violent in the past. He said he tried not to panic on Tuesday because there were "armed policemen around me."

Asked how often he had become violent, he said "a lot," but he declined to provide details.

The South African government said at a press conference Thursday that officials were "trying to establish what happened with the sign language interpreter."

Hendrietta Bogopane-Zulu, the South African deputy minister for women, children and persons with disability, said that the government was investigating the whether the interpreter had been vetted before the memorial.

Jackson Mthembu, a spokesman for the ruling National African Congress party, told NBC News Thursday that he was concerned that Jantjie's qualifications or medical history had apparently not been taken into account before he was given close access to world leaders at the government-organized event.

"We are not aware that he was being treated for [schizophrenia]. He did not disclose it. That is another thing that is concerning to use because we are having this information for the first time," Mthembu said. "This man was close to many presidents, including our own. We are worried about when we have procured him for activities for our own services. That is what we are concerned about."

NBC News security analyst James Cavanaugh said it was troubling that there were so many questions about a person who had been granted face-to-face access to world leaders.

"There should not be a person there if that person is not completely vetted and they know exactly who they are," said Cavanaugh, a retired special agent-in-charge for  the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). "There are too many terrorists in that region of the world to take even the slightest chance to have a person that's not really known that close to world leaders."

In an email response to The Associated Press, Secret Service spokesman Ed Donovan added that "agreed-upon security measures between the U.S. Secret Service and South African government security officials were in place" during the service.

White House spokesman Josh Earnest played down the incident. 

"It's a shame that ... a service that was dedicated to honoring the life and celebrating the legacy of one of the great leaders of the 20th century has gotten distracted by this and a couple of other issues that are far less important than the legacy of Nelson Mandela," he told reporters on Wednesday.

Jantjie told Talk Radio 702 he was employed by a company called SA Interpreters. The company declined to comment when contacted by NBC News on Thursday.

Bogopane-Zulu, the government minister, said officials have tried to track down SA Interpreters but that the owners "have vanished into thin air."

According to Jantjie, he was paid about $85 for appearing the Mandela memorial.

The Deaf Federation of South Africa said on Wednesday that it had submitted a formal complaint to the ANC about Jantjie's interpretation after an event in 2012.

But Mthembu, the ANC spokesman, said he was not aware of the complaint and that the party was looking into the matter.

Mthembu said that although Jantjie had appeared as a sign language interpreter at  political events on a voluntary basis in the past, the party had not recommended him to the government for the Mandela memorial.

"ANC will look at our procedures in view of what has transpired and in view of some information that is now in the public domain," he added.

NBC News' Chapman Bell, The Associated Press and Reuters contributed to this report.