A former Kosovo rebel commander has gone on trial in the Hague, accused of war crimes.

Salih Mustafa has been accused of murdering and torturing suspected collaborators during Kosovo’s 1998-99 war for independence from Serbia.

Prosecutors say there is irrefutable evidence that the former rebel fighter is guilty of the torture of at least six people and the murder of another.

Salih Mustafa was arrested one year ago in Kosovo and sent to the Netherlands to stand trial at the European Union-backed Kosovo Specialist Chambers.

It will be the first trial heard at the court, a branch of Kosovo’s legal system that was set up specifically to deal with allegations of war crimes.

Lead prosecutor Jack Smith stressed that the charges did not target the people of Kosovo or their struggle for independence.

Mustafa is charged with the war crimes of arbitrary detention, cruel treatment, six cases of torture, and the murder of one person at a detention compound in Zllash in April 1999.

The victims were accused by Kosovo Liberation Army (KLA) fighters of collaborating with Serbs or not supporting the KLA, according to his indictment.

Mustafa has pleaded not guilty to all charges and angered victims’ lawyers by leaving court after the prosecution’s opening statement.

“We perceive this as a clear disregard and disrespect for victims,” lawyer Anni Pues said.

Victims have alleged that a number of war crimes were committed as ethnic Albanian rebels united in the Kosovo Liberation Army fought a bloody conflict to break away from Serbia in 1998-99.

Those held at the detention center Mustafa ran were forced to sleep on the filthy floor of a barn and given insufficient food, water, and medical treatment for injuries sustained in brutal beatings, prosecutors allege.

A 2011 report by the Council of Europe included accusations that rebel fighters trafficked human organs taken from prisoners and killed Serbs and fellow ethnic Albanians they considered collaborators.

Pues said victims have been waiting more than two decades for accountability for the crimes.

“None of the wounds inflicted in 1999 have healed,” she said on Wednesday.

Among other former rebel commanders in custody awaiting trial are former Kosovo President Hashim Thaci, who resigned from office last year to defend himself against war crimes charges in The Hague.

Most of the people who died in the Kosovo war were ethnic Albanians. A 78-day NATO air campaign against Serbian troops ended the fighting. KLA fighters are widely considered heroes in their home country.

Several Serbs have been prosecuted at a former U.N. war crimes tribunal for their roles in atrocities in the Kosovo war.