The six medical workers held for eight years in a Libyan prison on false charges of deliberately infecting hundreds of children with HIV were finally freed last week. But Libya's cynical insistence on their guilt is casting a pall over this long-awaited event.

Late in the negotiations that saw the medics' sentences commuted from the death penalty to life imprisonment followed by their extradition to Bulgaria, Libya refused a request for the final settlement to state that it did not represent an admission of guilt. When Bulgaria freed the six, Baghdadi Mahmudi, Libya's prime minister, denounced the pardon as a “betrayal”, arguing that the medics should have served life sentences. It is time for Libya to end this charade.

The six's only crime was to be in the wrong place at the wrong time. From the outset they were pawns in a larger geopolitical game in which human rights and justice played second fiddle to Realpolitik — in this case, Libya's position as a major oil exporter and its utility as an ally in the 'war against terror'. That the medics are out at all is a tribute to the patience and determination of a handful of European diplomats.

An important supporting role was played by scientists who took up the medics' cause, including Nobel laureate Rich Roberts of New England Biolabs; Vittorio Colizzi, an AIDS researcher at Tor Vergata University in Rome; and Luc Montagnier, whose group in Paris discovered HIV. They all persistently dissected the emptiness of the prosecution case, showed multiple avenues of evidence pointing to a hospital infection as the true cause of the outbreak and campaigned tirelessly.

The scientists quickly learned that effectiveness in such matters demanded tight liaison with defence lawyers and human-rights groups. One-off appeals and letters of protest can have some impact in raising public awareness, but effective advocacy requires sustained action, clear objectives and a strategy to achieve them.

When scientists upped the pressure in the run-up to the trial last autumn (see Nature 444, 146; doi:10.1038/444146a 2006), calling for the scientific evidence to be heard, some observers argued the approach was naive. After all, the court had consistently refused international expertise in the case. But the strategy had already been recognized by the medics' lawyers and human-rights groups as the best card to play.

Had Libya allowed the scientific evidence to be heard in court, the prosecution case would have collapsed. As was always more likely, it refused this, thus exposing the trial as a sham and providing a useful lever for public, and hence political, opinion.

At other times it was necessary for the scientists and human-rights activists to protect the prisoners' interests by showing discretion in their public statements. It was known from diplomatic sources, for example, that Libya's Supreme Court would uphold the death-penalty verdicts — as it did on 11 July — but that these would be commuted soon afterwards. Had there been huge public outrage at the initial verdict, the commuting of the sentences might have been derailed, so those involved agreed that public reaction should be restrained until the final decision.

The six medics were not given a fair trial and scientific evidence that would have exonerated them was ignored.

Now that the medics are free, such restraint is unnecessary. The 1998 outbreak was a triple tragedy: for the six, for the infected children and for human rights. The six were not given a fair trial, prosecution evidence was fabricated and scientific evidence that would have exonerated the medics was ignored. Their trials were a mockery of justice.

Progressive elements within Libya want this truth to come out. Seif al-Islam Gaddafi, son of Libyan leader Muammar al-Gaddafi, played a significant role in resolving the case through one of his charities. He is convinced that the outbreak was an accident, and wants Libya to face up to its AIDS problem and to promote health care.

Libya has, unfortunately, won plaudits in parts of the Arab world for the way it has played its hand, winning normalization of its political and economic ties with the European Union (EU) and much else besides for releasing the six. The EU and the United States should make further normalization contingent on the Libyan government owning up to the real facts of the case, and exonerating the six.