Mihajlo Hrastov, a former special forces policeman, was sentenced to four years' jail for killing 13 prisoners-of-war in 1991 after six trials and the longest war crimes process in Croatian judicial history.
Croatia's Supreme Court issued the sentence on Friday, blaming the courts for the length of the judicial process.
However, the sentence is still not definitive, because the possibilities for an appeal still remains.
This may come either from the prosecution, which complained that the sentence was too short, or from the defence, which has already indicated that request an acquittal.
Hrastov was found guilty of having killed 13 reservists of the Yugoslav People's Army, JNA, and of having wounded two others on September 21, 1991, in the central town of Karlovac.
The trial chamber concluded that he killed them after they surrendered. "There was no self-defence, nor did the prisoners try to escape, so the shooting could not be justified by international laws," Judge Zarko Dundovic said.
The indictee had perpetrated "the war crime of killing prisoners-of-war after they had laid down their arms and surrendered", Dundovic noted.
He explained the relatively brief sentence of four years on the grounds that Hrastov had never committed any other illegal acts and was 70 per cent invalided with PTSP, while his wife was also ill.
Dundovic also said that "the passage of time is also an important circumstance", describing the defendant as "also some kind of victim of such a long trial".
The trial has been one of the longest in Croatian judicial history. The suspect has been released three times now and twice convicted.
Last May a court confirmed a sentence of seven years and Hrastov started to serve his term. But the Constitutional Court then overturned the verdict last November, because the Supreme Court, which had convicted Hrastov, had failed to publish the sentence.
The case remains an emotive one for many Croats. In Karlovac, Hrastov is widely regarded as a war hero.
Karlovac, which lay on the frontline during the Croatian war for independence in 1991, was heavily damaged by Serb bombardment.
Local war veterans’ organisations have condemned the trial, while human rights NGOs warned that it represents a major test for the Croatian judiciary.
Hrastov was first released in September 1992 by the Karlovac County Court. In March 2007, a Karlovac court released him for the third time, after the Supreme Court struck down two earlier acquittals before the Karlovac court.
After that, the Supreme Court took on the case and in May 2009, Hrastov was jailed for eight years.
The appeal chamber reduced the sentence to seven years last January, and Hrastov started to serve the punishment.
That was when the Constitutional Court struck down the sentence, saying that the failure to publish the decision had breached Hrastov’s human rights.
Hrastov still will not go to prison until the sentence becomes definitive, however.