Milan Spanovic’s lawyer said the war crimes charges were false and complained that his client was being accused of petty crimes such as “lawnmower theft”.
Spanovic was indicted for war crimes committed during a Serb attack on the village of Maja in central Croatia in 1991.
In 1993, together with 18 more former members of Serb forces in Croatia, he was convicted in absentia to 20 years in prison.
He was extradited to Croatia from Britain in 2009, then retried and given a much lower sentence of three and a half years in prison.
But the Croatian supreme court annulled that sentence "because of grave violations of criminal procedure".
Spanovic's lawyer Silvije Degen said at the beginning of the third trial on Thursday that the case was based on "unfounded indictments which were filed 20 years ago".
He said the case shoud be dropped because everyone else accused of being involved in the attack has already been amnestied and some of the accusations levelled against Spanovic were ridiculous.
"Spanovic is indicted for ordinary lawnmower theft," Degen said.
One of two witnesses in court on Thursday confirmed that Spanovic stole a motor mower from his yard during the attack on the village in 1991.
The other witness couldn't confirm that Spanovic was shooting and looting in the village.
In the early 1990s, it was common practice by the Croatian judiciary to organise mass trials of Serbs in their absence.
Many of those trials were politically motivated and intended to relieve victims’ families’ anger about the lack of prosecutions of war crimes perpetrators.
Croatia has issued more than 600 arrest warrants in relation to war crimes and held about 400 in absentia trials, almost entirely of Serbs.
State-appointed defence lawyers routinely did little to represent their absent clients.
The first Spanovic trial was considered an example of this practice, which has been criticised by the OSCE, Amnesty International and Human Rights Watch.
After 2000, new state prosecutor Mladen Bajic abolished the practice and ordered the revision of all war crimes indictments filed during the 1990s.
Many of those indictments were withdrawn after the revision.