The European Court of Human Rights has ruled that Turkey's trial five years ago of Kurdish rebel leader Abdullah Ocalan was unfair.
A panel of ECHR judges, reaching their verdict by 11 to 6, said in a statement that Ocalan had not had proper access to legal counsel or the facilities needed for his defence.
They added that he was not tried by an independent and impartial tribunal.
The Ankara government has signalled that Ocalan could indeed be tried again.
But it moved quickly to assure Turks who revile him as a terrorist bent on dismembering their nation that he would not walk free.
While it is not binding, the ECHR ruling could cause problems for the Turkish government, which is trying to meet the European Union's entry conditions on human rights.
Ocalan was jailed for his perceived role in a separatist revolt in which at least 30,000 people died.
