It was only the photograph of her granddaughter that kept Snezhana Dimitrova going.

The picture of the little girl were her comfort through eight terrifying years in a Libyan jail, three of them under sentence of death by firing squad.

The 54-year-old nurse had gone to the North African country to pursue her vocation as a childcare specialist.

But after forced confessions arising from alleged torture, including beatings and electric shocks, she was convicted, along with five colleagues, of deliberately infecting 438 Libyan children with the Aids virus.

Yesterday morning on the tarmac at Sofia airport, Mrs Dimitrova tearfully hugged her two children and the seven-year-old granddaughter she thought she would never live to see.

“I waited so long for this moment,” she said as the Bulgarian capital came to a standstill to savour the news.

Within an hour she and her colleagues — four other Bulgarian nurses and an Egyptian-born trainee doctor — had received a presidential pardon.

“I still cannot believe that I am standing on Bulgarian soil,” said Kristiana Valcheva, the nurse accused of being the ringleader of a Mossad plot to undermine Libya.

“We were told the news at 4am and we left the jail at 5.45am to board the plane,” she said. “Now I will try to get my previous life back.”

It will not be easy. All six claim to have been tortured. Mrs Valcheva suffered electric shocks at least ten times, she says, during attempts to wring a signed confession from her. All have missed children growing up and parents growing old.

Nasya Nenova, at 41 the youngest nurse, and said to be the most sensitive of the group, tried to commit suicide by slashing her wrists with a broken bottle to avoid interrogations.

Bulgarians have asked repeatedly why their citizens were singled out for prosecution. There were other foreign nationals working at Benghazi’s al-Fateh paediatric hospital, which employed nurses from as far afield as France and the Philippines. But when the infection of hundreds of children with HIV was discovered in the 1990s, Bulgarians believe that their country was vulnerable to Libya’s search for a scapegoat to cover up poor hygiene and the re-use of needles.

Georgi Milkov, a journalist who has followed the case, said: “Bulgaria at this time had become a big friend of the US. The Libyans wanted to find somebody from abroad to blame because it much easier to explain in such a society that the problem was coming from Mossad or the CIA.”

In all, 19 foreign medics were arrested in 1999 but only five Bulgarian nurses, a Bulgarian doctor married to one of them and the trainee doctor were put on trial along with eight Libyans. During 2000, as the trial dragged on, the first allegations of torture were made by the nurses’ families.

In court, evidence was presented by Luc Montagnier, the French doctor who first isolated the HIV virus in the Benghazi hospital, that the infections had taken place before most of the Bulgarians had arrived. But it cut no ice with the Libyan judges and the five nurses and trainee doctor were found guilty in May 2004.

On the day his wife was sentenced to death, Zdravko Georgiev, the husband of Mrs Valcheva, was convicted of currency smuggling but freed because he had already spent four years in prison, much of it in a cell measuring 9¾ft (3m) by 5½ft with up to eight people at a time.

“I could not lie down to sleep for two years — I could only sit. You cannot imagine it. In the summer it got so hot, people were passing out,” he said yesterday after travelling back to Sofia with the freed nurses.

He said that he had four teeth knocked out by interrogators but added that it was nothing compared with the electric shocks given to the nurses. “They tortured and treated them like animals — in fact, you would not treat animals like that,” he said. Charges of torture were brought against nine policemen and a Libyan doctor in 2005. They were acquitted.

Even though Dr Georgiev was released, he was banned from leaving the country. He has spent the past three years living in the Bulgarian embassy in Tripoli, visiting his wife on Thursdays.

By late 2004 Colonel Gaddafi began to see the medics as an opportunity. The prisoners became a bargaining chip in Libya’s emergence from years of international isolation.

The nurses’ detention in 1999 came months after Libya, under huge international pressure, had handed over Abdul Baset Ali al-Megrahi, the man convicted over the Lockerbie bombing. They were convicted more than a year after his first appeal was rejected.

Libya developed three main demands for the medics’ release: financial compensation, international recognition and another review of the al-Megrahi case.

By last weekend, all three had come together. A compensation package was arranged of $1 million (£485 million) for the families of every HIV-infected child, a review of Libya’s relations with the EU and a review of the Lockerbie conviction, although the British Government denied any link.

As the nurses stepped off the French presidential aircraft they returned to a country that market reforms and privatisations has changed beyond recognition. But the biggest changes are in the shattered families. Snezhana Dimitrova’s father, Ivan Klisurski, suffered a stroke after the confirmation of the death sentence on his daughter in 2006 and was not sure he would live to see her again.

Georgi Parvanov, the Bulgarian President, pledged that Bulgaria would continue to support the Aids-stricken children despite the ordeal. In a moving address to the medics, he said: “I know that you lived through monstrous moments. More than eight years of your lives passed in suffering. But you survived. You are the real winners in this battle for freedom.”

From sedition to statecraft

— Colonel Gaddafi came to power in a 1969 coup, swept away the monarchy, nationalised industry and expelled foreign troops. A later “people’s revolution” solidified his control, accelerating Libya’s economic decline

— He dreamt of a unified Arab state as a counterweight to perceived Western enemies. Attempts to merge Libya with Egypt, Syria and Tunisia in different combinations all failed

— Libyan security forces were linked to the 1988 Lockerbie disaster and an attack on a French airliner in 1989. US air strikes and UN sanctions followed Britain broke off relations after a policewoman was shot dead in London during anti-Gaddafi protests

— In 2003 Libya admitted the Lockerbie bombing. UN sanctions were lifted and UK diplomatic relations restored

— Tony Blair welcomed Gaddafi back to the international fold in 2003, with first visit by a British leader since 1943. Relations with US normalised last year

Sources: Global Security; UK Foreign and Commonwealth Office

Set free

Valia Cherveniashka 52, mother of two daughters, from Biala Slatina, a small town in northwest Bulgaria. Worked in a hospital in the Libyan city of Tarbouha between 1984 and 1997, before moving to the al-Fateh hospital in Benghazi. Her husband, Emil Uzunov, was the first to bring the arrest of the medics to public attention in Bulgaria.

Snezhana Dimitrova 54, worked as a nurse in Sofia and arrested six months after her arrival at the al-Fateh hospital in 1998. A diabetic who suffered a nervous breakdown in 2005 and broke her leg last year. She has a daughter, a son and a seven-year-old granddaughter whom she knew only through photographs.

Nasya Nenova 41, worked at a hospital in the eastern Bulgarian city of Sliven before moving to Libya in 1998. After complaining of torture, she withdrew her confession and tried to commit suicide. Married with a son, who was a schoolboy when she left Bulgaria and is now at university in France.

Valentina Siropoulo 48, worked in the intensive care unit of Pazardjik hospital, Bulgaria, before arriving in Libya in February 1998 to earn more money to send her son to university. She last saw him in 2003 and he now has a master’s degree from Sofia Technical University. Her face has been left partially paralysed, allegedly by torture.

Kristiana Valcheva 48, went to Libya with her husband, Dr Zdravko Georgiev, 58, in 1991. Accused of being the Mossad-inspired organiser of the HIV plot. Husband released on the day she received the death penalty in 2004. He stayed in the Bulgarian Embassy in Tripoli and visited her every Thursday.

Ashraf Alhajouj 38, born in Egypt. Was a trainee doctor at the al-Fateh hospital. It took his family ten months to find the jail where he was being held. His sister and Palestinian father fled Libya in 2005 and were granted refugee status in the Netherlands. He became a Bulgarian citizen last month.

Times Recommends

• No cause for celebration in crushed Sarajevo
• Jazz funeral for the final victims of Katrina
• French fined for 'insulting' civil servants