A spokesman said officials were looking into how Thamsanqa Jantjie was selected to interpret at the memorial on Tuesday during which he stood near US president Barack Obama and other leaders.
Mr Jantjie outraged deaf people by making signs they said amounted to gibberish.
A South African TV news outlet, eNCA, reported that Mr Jantjie faced a murder charge a decade ago, but was unclear if the case was concluded. He also reportedly faced other criminal charges.
Asked about the charge, Mr Jantjie turned and walked away without commenting.
A top United States official said “we’re all very upset” about the bogus sign language interpreter who appeared just three feet from Mr Obama at the memorial ceremony
US Assistant Secretary of State for African Affairs Linda Thomas-Greenfield said that officials were concerned about security and how the interpreter could have got so close to world leaders.
Mr Jantjie said on Thursday he has been violent in the past and hallucinated during the memorial service as he was gesturing incoherently.
Ms Thomas-Greenfield also said officials are dismayed because the people who need sign language weren’t able to understand what was said at the ceremony. She called the problem “extraordinarily sad”.
Yesterday, thousands were turned away as they tried to say farewell to Nelson Mandela, leaving them fighting back tears of disappointment.
An estimated 100,000 mourners lined up in Pretoria to view Mr Mandela, but officials had to send away about half of the crowd.
Several hundred mourners eager to pay their last respects broke through police barriers and stormed up toward the Union Buildings toward the coffin.
An AP reporter saw police chase people several hundred metres to stop them.
There was no violence and police peacefully brought them back in line.
Fulfilling Mandela’s goals: Page 15.