A man has been arrested on suspicion of 77 murders after telling a public inquiry he started last August's deadly fire in a Johannesburg building.
The 29-year-old confessed while giving evidence at the inquiry, police said.
Last year fire gutted the Usindiso building in Marshalltown, where many poor people were living, claiming 77 lives and leaving many injured.
The tragedy highlighted the issue of buildings abandoned or neglected by their owners in South Africa.
A South African Police Service spokesperson said the suspect, who cannot be identified, is expected to appear in court soon.
He is also expected to face charges of arson and 120 counts of attempted murder.
The individual confessed to "being involved in starting the tragic fire" while giving evidence during a session of the inquiry, police said.
The Usindiso building was home to hundreds of people, some of the poorest people in South African society.
Such abandoned buildings are often left without basic services such as water and electricity or fire safety measures - and are sometimes "hijacked" or taken over by criminals who make demands on residents.
The City of Johannesburg owned the Usindiso building and on Monday, Mayor Kabelo Gwamanda said 188 "bad" buildings were being investigated, with 134 of them in the inner city.
The public inquiry into the disaster is taking evidence on the fire and the wider issue of unsafe buildings and is due to report later this year.
Shortly after the fire President Cyril Ramaphosa said it had been a "wake-up call" for South Africa and the city of Johannesburg had to get to grips with issues around housing and services in Johannesburg's inner city.
South Africa faces a chronic housing shortage, with an estimated 15,000 people believed to be homeless in Johannesburg.
