A former fighter with the Kosovo Liberation Army was responsible for the murder of one person and the illegal detention and torture of nearly 20 more during his country’s war for independence from Serbia, an international prosecutor has said at the start of a war crimes trial.

The defendant, Pjeter Shala, insists he is innocent and has pleaded not guilty to four charges of war crimes at the European Union-backed Kosovo Specialist Chambers, a court that is part of the Kosovo legal system but based in the Netherlands.

Later this year, the court is scheduled to begin the trial of Kosovo ex-President Hashim Thaci on charges including murder for his alleged role in atrocities as a guerrilla leader during the 1998-99 war. He denies all charges.

Alex Whiting, an American lawyer leading a prosecution office linked to the court, told a three-judge panel there is enough evidence to convict Shala despite what he described as a pervasive climate of witness intimidation in Kosovo.

“We are confident that the evidence that will be presented during this trial will establish beyond a reasonable doubt that Mr Shala is criminally responsible for the crimes charged in the indictment,” he said.

Shala, who was arrested nearly two years ago in Belgium, told judges: “Everything is fabricated” as he insisted he is “fully not guilty”.

He is accused of mistreating ethnic Albanian Kosovars who were perceived as spies or collaborators with Serb forces at a makeshift detention centre at a metal works in Kukes, northern Albania, in May and June 1999.

Mr Whiting said Shala took part in the brutal beating of detainees, leaving them “covered in blood, suffering from broken bones or unable to walk”.

Shala, 59, was also “part of the group that murdered one of the detainees by beating him repeatedly and severely and shooting him in the leg, causing him to bleed to death over a period of many hours,” Mr Whiting said.

Most of the people who died in the 1998-1999 war in Kosovo were ethnic Albanians. A 78-day Nato air campaign against Serbian troops ended the fighting but tensions between Kosovo and Serbia remain tense.