By Gabriel Partos
BBC South-East Europe analyst
Libya's High Court of Appeal has started its hearings into the case of five Bulgarian nurses and a Palestinian doctor who have been sentenced to death for infecting more than 400 children with the potentially deadly virus, HIV, in a hospital in Benghazi.
Defence lawyers say the children already had the virus which causes Aids
The defendants, who have been protesting their innocence, have been in jail since 1999.
Attempts to ensure their freedom have concentrated on diplomatic moves as well as potential financial deals.
But what chance is there for their release, given that Libya's leader, Muammar Gaddafi, appeared to rule out it happening under pressure from the West?
Bulgarian Foreign Minister Solomon Passy has been making use of his latest visit to the US at least, in part, to lobby for further international support for Bulgaria's attempts to secure the release of the five nurses.
In the past few days, Mr Passy has had an opportunity to discuss the issue with US Secretary of State Condoleezza Rice and United Nations Secretary General Kofi Annan.
Gaddafi's Libya has not executed anyone in nine years
Bulgaria has previously received the backing of both the US and the UN - as well as the European Union, which the country is set to join in three years' time.
There was widespread international condemnation for Tripoli when the five Bulgarian nurses and the Palestinian doctor were sentenced to death a year ago.
That was partly because the convictions went in the face of expert witness testimony which argued that the HIV infections, caused by poor hygiene, had predated the defendants' arrival at the Benghazi hospital.
The accused also argued that their earlier confessions - which they subsequently withdrew - had been extracted through torture.
Two months ago nine Libyan police officers and a physician appeared in court on charges of torture relating to this case.
These torture allegations may now be taken into account at the hearings before Libya's High Court of Appeal, which court officials said will last until the end of May.
It was in the run-up to these hearings that Sofia has renewed its diplomatic offensive in the US and elsewhere.
The medics have been sentenced to death by firing squad
But Bulgaria has been treading carefully on the international stage, preferring quiet diplomacy to high-profile rhetoric.
As Bulgarian Prime Minister Simeon Saxe-Coburg put it last week, the less the issue is politicised, the better it is for the accused and their chances of release.
Mr Saxe-Coburg's remarks came as the Bulgarian parliament decided not to adopt a formal motion calling for the release of the accused.
The debate came just a couple of days after Mr Gaddafi had told an Arab League summit in Algiers that the defendants would not be set free in response to Western pressure.
But he made a more conciliatory gesture a few hours later when he invited Bulgarian President Georgi Parvanov to visit Libya.
Libya's leader does not want to be seen to be acting under international pressure.
But Libya's international rehabilitation from its previous pariah status cannot be completed until an acceptable solution is found to the fate of those convicted over the Benghazi mass HIV infections case.
Libyan officials have suggested that the price for their release might be Bulgaria paying compensation to the families of the 47 children who have died and the more than 400 infected with the HIV virus.
Sofia is opposed to that on several grounds.
It would amount to an acceptance of responsibility for something neither the Bulgarian nurses nor Bulgaria were to blame for.
And it would suggest an equivalence with Libya's responsibility for the Lockerbie bombing of 1988 - the killings of hundreds of passengers on an American airliner - for which Tripoli is now finally paying compensation.
On the other hand, Sofia may come under pressure to make a gesture - perhaps behind the scenes - by writing off some of Libya's debt.
It has much at stake, not least of which is the safety and continued employment of several thousand Bulgarians who currently work in Libya.
And with parliamentary elections just a few months away, securing the release of the Bulgarian nurses would be a significant political achievement.