South Africa's government has been confronted with a new and chilling allegation about the bogus sign language interpreter at Nelson Mandela's memorial. He was reportedly accused of murder 10 years ago.

Officials said they were investigating the revelation by the national eNCA TV news station. But they were unable, or unwilling, to explain why a man who says he is schizophrenic with violent tendencies was allowed to get within arm's length of US president Barack Obama and other world leaders.

Investigators probing Thamsanqa Jantjie "will compile a comprehensive report", said top government spokeswoman Phumla Williams. But she did not say how long the investigation would take and insisted details would not be released until it was completed.

"We are not going to sweep it under the carpet," Ms Williams said. "We want to own up if there is a mistake, but we don't want to be dishonest" to Mr Jantjie.

An Associated Press reporter found Mr Jantjie at a makeshift bar owned by his cousin on the outskirts of Soweto yesterday, near his concrete house close to shacks and an illegal dump where goats pick at grass between the trash. Asked about the murder allegation, Mr Jantjie turned and walked away without saying anything.

A day earlier, he told the AP that he had been violent "a lot" in the past, has schizophrenia and hallucinated during the Mandela memorial that angels were descending into the stadium. He also apologised for his performance, but defended his interpreting as "the best in the world".

His assertion was ridiculed by deaf advocates who said he did not know how to sign "Mandela" or "thank you".

The outcome of the reported murder case that eNCA said dated from 2003 was unclear, and the television report did not disclose any details.

There were no records of a murder case involving Mr Jantjie at South Africa's National Prosecuting Authority, but spokesman Nathi Mncube said that does not necessarily mean Mr Jantjie was never a suspect.

"I cannot confirm that the guy was charged, but I cannot deny it, either," he said. "There are no records right now."

Mr Jantjie also faced other lesser criminal charges in the past, eNCA reported. In the interview with the AP, he blamed his past violent episodes on his schizophrenia, but declined to provide details.

The fiasco surrounding the use of Mr Jantjie to provide sign language translation before a worldwide television audience has turned into an international embarrassment for South Africa, whose ruling party, the African National Congress (ANC), and president, Jacob Zuma, have already lost popularity because of corruption scandals and other public grievances.

But the ANC is far more powerful than the opposition and Mr Zuma, who was booed at the Mandela memorial, is likely to be its candidate in elections next year.

The US assistant secretary of state for African affairs, Linda Thomas-Greenfield, said that "we're all very upset" about Mr Jantjie, who was just 3ft from Mr Obama at the memorial service for Mandela, who died on December 5 at 95.

Ms Thomas-Greenfield told reporters in Kenya that US officials are concerned about security and how Mr Jantjie could have gotten so close to world leaders. She said officials were also dismayed because people watching around the world who needed sign language were not able to understand what was said at the ceremony. She called the incident "extraordinarily sad".

South Africa's arts and culture minister Paul Mashatile apologised for the use of Mr Jantjie yesterday, marking the second apology from the government in two days, and said reforms must be implemented to ensure such an incident does not happen again.

"Without passing judgment, nobody should be allowed to undermine our languages. We sincerely apologise to the deaf community and to all South Africans for any offence that may have been suffered," Mr Mashatile said in a statement. He did not comment on who was responsible for hiring the sign interpreter.

Four government departments involved in organising the historic memorial service distanced themselves from the hiring of Mr Jantjie, telling the AP they had no contact with him. A fifth government agency, the Department of Public Works, declined to comment.

Ms Williams said the investigation would include trying to determine who hired Mr Jantjie or the company he said he worked for. She did not say how long the probe might take, and police spokesman Lieutenant General Solomon Mogale said there would be no additional information released until after Mandela's funeral tomorrow in his hometown of Qunu.

The government is also trying to determine how Jantjie received security clearance and what vetting of his background - if any - took place. Officials at the State Security Agency, in charge of security for the event, have not commented publicly.

The government says the owners of the interpreting company have disappeared, and the AP was unable to track down the school where Mr Jantjie said he studied signing for a year. An online search for the school, which Mr Jantjie said was called Komani and located in Eastern Cape Province, turned up nothing.

Ingrid Parkin, principal of the St Vincent School for the Deaf in Johannesburg, said she and other advocates for the deaf had never heard of the school. She added that there are no known sign language institutes in the province.

The Star newspaper of Johannesburg reported that Mr Jantjie said he studied sign language interpretation in Britain at the University of Tecturers.

"We're not aware of that university," said Emma Mortimer, communications director of Signature, a charity that awards qualifications in deaf and deaf-blind communication techniques.

Even if he had studied in the United Kingdom, Ms Mortimer said that would not necessarily qualify him to work in South Africa because the country's two sign languages are different.

"It would be like you going to France and speaking English," she said.