"Most of the Zimbabweans want to leave. It is better at home than here," said the former teacher who was chased out of his home by a mob early Sunday.
"It's spreading like wildfire and the police and the army can't control it," Ziso said, as he tried to help register about 500 people who sought refuge at the police station in Johannesburg's Cleveland area.
It was a scene repeated in other poor suburbs around the city. Angry residents accused foreigners - many of them Zimbabweans who had fled their own country's economic collapse - of taking scarce jobs and housing.
President Thabo Mbeki said Sunday that he would set up a panel of experts to investigate. African National Congress President Jacob Zuma, who is likely to succeed Mbeki next year, condemned the attacks.
"We cannot allow South Africa to be famous for xenophobia," Zuma told a conference in Pretoria.
The weekend attacks came as the government tries to change South Africa's violent image ahead of the 2010 World Cup. South Africa has one of the highest crime rates in the world, recording an average of 50 murders each day.
Many in the ANC government took refuge in neighboring countries during apartheid and are deeply embarrassed by the current violence, which has targeted immigrants who came to South Africa from other nations in the region.
Police spokesman Govindsamy Mariemuthoo said 12 people were killed. He said 200 people had been arrested on charges ranging from rape to robbery and public violence.
The Red Cross said at least 3,000 people were left destitute.
Police said the worst violence erupted after midnight Saturday in Cleveland and other run-down inner city areas that are home to many immigrants. Two of the victims were burned and three others beaten to death. More than 50 were taken to hospitals with gunshot and stab wounds.
The situation remained tense along the main street through Cleveland and police had to use tear gas to disperse stick-wielding crowds trying to loot shops.
Photographs supplied by local newspapers captured horrific images of a man who was set on fire after a tire soaked in gasoline was put around his neck. There was no immediate word on his condition.
One of the demonstrators in Cleveland, Michael Khondwane, said foreigners were to blame for South Africa's drug and crime scourge. He said the violence would send them "the message that they must go."
Johannesburg is South Africa's economic hub and home to hundreds of thousands of immigrants. Many of them are illegal, but many have also been here for more than a decade and possess South African identity documents.
There has been sporadic anti-foreigner violence for months, mainly aimed at stores run by Somalis accused of undercutting local storeowners, but nothing that compares to the violence over the weekend.
Eric Goemaere, the head of Medecins Sans Frontieres in South Africa, said his staff was helping to treat people with bullet wounds and back injuries from being thrown out of windows.
He called on the South African government to declare Zimbabweans as refugees and give them proper protection. "It's a crisis," he said.
There are believed to be up to 3 million Zimbabweans living in neighboring South Africa who have fled the economic and political turmoil in their homeland.
Massive inflation, food and fuel shortages have sent increasing numbers of Zimbabweans to South Africa, Zambia, Botswana, Mozambique and Namibia in search of business and basic commodities - or whole new lives.
Zimbabwe's opposition also has cited mounting violence and intimidation targeting its supporters since the country's disputed March 29 presidential election. A runoff between longtime ruler Robert Mugabe and opposition leader Morgan Tsvangirai is set for June 27.
At the downtown Jeppe police station, large tents and water tanks were being offloaded to help another group of 500 people who sought shelter. Dazed-looking women sat huddled close to piles of blankets and clothes while men kept watch over fridges, bicycles, TVs and other belongings.
Mozambican Bevinda Komati's family including her 11-year-old niece and a 1-month-old baby had to be rescued by police when a mob attacked her brother's small store in downtown Johannesburg.
"We had to hide in the back. They were breaking windows and throwing stones. We didn't know what to do. Luckily, the police came and saved us."
The 26-year-old has been living in South Africa since 1988. Her niece was born here.
"We have lived with these people every day. I don't know why they are doing this," she said.