It was the latest conviction in the trial of the informer and two soldiers accused of being rogue elements within the security forces targeting armed Kurdish rebels who have led a bloody campaign since 1984 for Kurdish self-rule in the region.

The court in the eastern city of Van jailed Veysel Ates -- described in the indictment as a former member of the Kurdistan Worker's Party (PKK) who turned informer in 2004 -- for nearly 40 years for the November 2005 bomb attack against a bookstore in Semdinli, in Hakkari province.

The same court had sentenced two gendarmerie sergeants to similar terms in June. Their sentences are currently under appeal.

The indictement had called for life sentences for all three defendants.

The bombing of the bookstore owned by a former PKK militant suspected of still aiding the group killed one person and sparked deadly riots in the remote region that abuts Iraq and Iran.

The indictment described the attack as an act of provocation aiming to stir unrest among Kurds, discredit the government and undermine Turkey's bid to join the European Union.

The Van trial was widely seen as a test for Ankara to prove its commitment to the supremacy of law and shed light on rogue elements in the security forces who are accused of murder, extortion, kidnappings and drug smuggling.

The bombing was mentioned in a critical report published by the European Commission Wednesday as an example of insufficient civilian control over the security forces in Turkey and continuing army influence in politics despite reforms to limit the military's role in decision-making.