An unusual group of protestors gathered on the lawns of Pretoria's Union Buildings, the seat of the South African government.
By Barnaby Phillips
BBC Southern Africa correspondent
The men's families want the South African government to step in
There were about 150 people - black and white, men, women, and young children.
They sang the national anthem and carried placards that read, "Bring them back!" and, "What about human rights?"
These are the relatives and friends of the 85 suspected mercenaries who were allegedly involved in a plot to overthrow the government in the oil-rich West African state of Equatorial Guinea.
Fifteen of them are behind bars in Equatorial Guinea, the remainder are imprisoned in Zimbabwe, where their plane was stopped in March, allegedly en route to join their colleagues in the coup plot.
The families and friends have waited anxiously for two months, but now they have had enough, and they want the South African government to intervene.
Reports that the men could face execution in Equatorial Guinea have spurred the relatives into action.
'Chained and beaten'
Belinda du Toit is the wife of Nick du Toit, the alleged coup leader.
There are concerns that the men may not receive fair trials
She wept as she handed over a petition to a junior South African government official.
She told me, "I hope someone in the South African government will listen to our pleas."
"If our men must be tried let it happen here, where there is a fair, legal system. If they stay where they are now, I'm sure they won't get a fair trial."
But there is not much sign that the South African government is prepared to get involved. It says justice must take its course.
And in Zimbabwe the trial has begun - in a special prison court.
The suspects are often kept in chains, and their lawyer says they have been beaten.
Wrong side of history
The Zimbabwean authorities say that when they stopped the plane carrying the suspected mercenaries, they discovered the men on board were planning to load it with weapons, before flying on to Equatorial Guinea.
In order to find out why men were prepared to get on board that plane to Zimbabwe, I drove out deep into the South African bush, to the fringes of the Kalahari desert, close to the Botswana border.
At the end of a long day's driving, I arrived in the bleak and remote town of Pomfret.
Originally built around an asbestos mine, it is here that South Africa dumped hundreds of black Angolan soldiers who fought for the old apartheid army.
They are the survivors of the notorious 32 Battalion, veterans of the bush wars of the 1970's and 80's.
But with apartheid gone, and the new ANC government far from sympathetic, they are stranded on the wrong side of history.
Shadowy security work
Pomfret is a strange and depressing town.
On the streets, the music is Angolan, the language Portuguese.
In the old hospital, I met a group of veterans living in squalid dormitories.
Veterans in Pomfret believe they have not been compensated
Joao dos Santos was injured in the war and is in a wheelchair, surviving on hand-outs, tormented by bitterness.
He said, "I am very, very sad. I am getting old in a wheelchair for nothing, I was used by the South African defence force and I am very angry with them."
But there are others here who are still fighting fit - and who need jobs.
When South African companies - some legitimate, others more shadowy - are looking for men to do security work, this is where they come.
In fact, more than 20 of the men imprisoned in Zimbabwe in connection with the coup plot are veterans of 32 battalion, with families living in Pomfret.
Victims of the past
Eduardo Tchimuichi is one of those behind bars in the Zimbabwean capital, Harare.
I went to meet his wife, Bibiana, and his daughter, Cecilia. They are confused and anxious.
"Eduardo told us he was going off to do a job, he didn't tell us where," said 26 year old Cecilia.
The family fears for its future with its main breadwinner behind bars
"Later I saw on TV that some men had been arrested in Zimbabwe, but it was only when we read a list of names in a newspaper that we knew Eduardo was there. It was a terrible shock."
Now the whole family is desperate for him to come home.
"He is the breadwinner here. Without him, how can we afford to send my sisters to school?" asked Cecilia.
The whole truth - whether or not there was a plot to stage a coup in Equatorial Guinea - may never emerge.
The brutal governments, there and in Zimbabwe, have their own agendas and may want to see all the men punished anyway.
But the families in Pomfret will tell you that these alleged mercenaries are also victims of South Africa's ugly past.