A year after an attack by a Serbian armed group in northern Kosovo’s Banjska killed a police officer, the trial is expected to begin on Wednesday at the Pristina Basic Court.

In all, 45 suspects have been indicted for the attack in September 2023, which Kosovo Serb businessman and politician Milan Radoicic later said he led and organised after he was identified in drone footage by Kosovo security officials.

The attack aggravated tensions between Kosovo and Serbia, and experts fear the trial could be complicated by the difficult nature of the relationship between the two.

Here’s what happened in Banjska and why the trial matters:

What happened in Banjska?

A group of Serbs, armed and masked, killed Kosovo police Sergeant Afrim Bunjaku and wounded two others when they ambushed a Kosovar police patrol in the village of Banjska near the Serbia-Kosovo border on September 24, 2023.

The group then fled to a nearby Orthodox monastery, and its members barricaded themselves in. A gun battle ensued with Kosovo police that lasted for hours. Three of the Serb assailants were killed, and dozens of the attackers fled to Serbia.

The police confiscated more than 1,000 of their weapons and pieces of equipment valued at more than 5 million euros (more than $5.5m).

Kosovar officials said the confiscated weapons were produced in Serbia and cannot be found on the open market. Based in part on the alleged origins of the weapons, Kosovo Prime Minister Albin Kurti and other Kosovar authorities have accused Serbia of masterminding the attack.

Who are the suspects and what are the charges against them?

The 45 defendants have been charged with “terrorism” and crimes against Kosovo’s constitutional order and security. The central accusation against them is that they were aiming to take over the northern part of Kosovo with the intent of annexing it to Serbia, according to the indictment filed in September.

Prosecutor Naim Abazi called the gunmen a “well-structured group” and said the investigations into the case were “one of the most complex that the prosecution has ever worked on”, according to the Balkan Insight news website.

Only three of the suspects remain in custody in Kosovo. The rest, including Radoicic, remain in Serbia.

On October 3, 2023, Serbian authorities arrested Radoicic for questioning. He denied guilt in his testimony to the Serbian prosecutor’s office. But previously in a letter read by his lawyer, he had admitted to personally organising the attack and denied the involvement of the Serbian government.

Why was the attack so significant?

The Banjska attack is one of the most violent incidents to occur in Kosovo since it declared independence from Serbia in 2008, a decade after a war between Serbian forces and ethnic Albanian secessionists that saw an Albanian Kosovar uprising against Belgrade’s rule.

The majority Serb population that lives in northern Kosovo does not recognise the country as a sovereign nation and views Belgrade as its capital. Over the years, there have been numerous clashes between Serbs on the one hand and Kosovo police and NATO-led peacekeepers on the other.

Since 2012, Belgrade and Pristina have been holding normalisation talks mediated by the European Union with the goal of joining the bloc, but the talks have broken down mostly over a deal to create an association of Serb-majority municipalities in northern Kosovo as some fear it would only create another mini-state.

Kosovo political leaders have accused Serbia of being behind the Banjska attack politically, materially and logistically. Kurti said Serbian President Aleksandar Vucic planned and ordered the attack “to destabilise” Kosovo with the goal of starting a war for more territorial gain.

Speaking to the media at a commemoration ceremony last month at the scene of the attack, Kurti maintained that Radoicic – who was at the time vice president of the Serb List, a Belgrade-supported political party in Kosovo – “was trained in Serbia and financed by Belgrade”.

Experts said the attack suggests a possible hardening in Serbia’s approach towards resolving differences with Kosovo.

The attack showed that “Serbia and its proxy groups have abandoned peaceful dialogue and have chosen hybrid warfare to achieve their political goals”, Gezim Visoka, associate professor of peace and conflict studies at Dublin City University, told Al Jazeera. Those goals, Visoka said, are to “force Kosovo and the international community to make further concessions in the EU-led talks for normalisation of relations, which have reached a stalemate due to fundamental disagreements”.

What has Serbia said?

Serbia has denied any role in the attack, and Radoicic has insisted that the Serbian government was not involved.

Vucic has instead accused Kurti of wanting to expel Serbs from Kosovo. After the attack, he said Kurti’s refusal to form an Association of Serb Municipalities – as part of a 2013 agreement between Belgrade and Pristina that would allocate Kosovo Serbs more autonomy – is what fuelled tensions leading to the violence in Banjska.

Journalist Branislav Krstic, a Serb from northern Kosovo, described the Banjska attack to Al Jazeera as “a gift for Pristina” — in that it helps strengthen Kosovo’s argument for keeping control over the Serb-majority north. The case, he said, adds to the “loss of sovereignty of Serbs in northern Kosovo”.

What’s expected during the trial?

Prosecution lawyers told the Kosovo daily Koha last month that they feared the trial would be prolonged, in part because most of the suspects are in Serbia.

Lawyer Kadri Osaj told Koha that their extradition from Serbia was unlikely due to a lack of legal cooperation between the two governments.

“The authorities of Serbia were directly and indirectly involved in the case, so I do not expect that these persons will be extradited to Kosovo,” Koha quoted Osaj as saying.

Visoka also said the fact that most suspects won’t physically be brought to trial complicates the process. Without Serbia’s cooperation and pressure from the West, it’s unlikely that Kosovo will be able to bring to justice the perpetrators of the attack, Visoka said.

“The trial is likely to reveal more about the political and operational nature of the attack than bring justice to the murdered police and the broader threat to Kosovo security,” he said.

Visoka added that while a speedy trial may be in the interest of the EU and international community to overcome the attack and bring the parties back to a dialogue, that might not suit Kosovo’s strategic interests.

It’s in Kosovo’s interest to use this case as an example to “ensure that its northern territory doesn’t again become a hotspot for organised crime and hybrid attacks”, he added.

“The attack also raises questions on the deeply embedded risks associated with Serb parallel and shadow structures that hide behind political parties, businesses and other groups who are all part of a grand agenda to undermine Kosovo’s sovereignty and prospects for becoming a fully recognised state [that is] part of the EU and a NATO member state,” Visoka said.

“A fast trial and ignorance of hidden Serb structures in the north of Kosovo is unlikely to make Kosovo a safe place.”