LYON, France (AP) — It wasn’t the deadliest attack in Europe linked to the Islamic State group, but it was among the most disturbing: One evening in 2016, an assailant killed two police officers in their family home, in front of their 3-year-old son.

On Monday, a trial opens in a French counterterrorism court over the attack in the Paris suburb of Magnanville.

The attacker, Larossi Abballa, was shot to death by police. According to court documents, he told police negotiators that he was responding to an IS leader’s call to “kill miscreants at home with their families.”

A childhood friend of Abballa’s, Mohamed Aberouz, is going on trial for complicity to terrorism-related murder, complicity to kidnapping and terrorist conspiracy. He faces up to life in prison if convicted.

The killings came amid a wave of attacks in France linked to the Islamic State group and had a lasting effect on police officers around France. Some moved, changed services or resigned to protect their loved ones after the Magnanville killings.

According to court documents, Abballa broke into the home of police officers Jessica Schneider and Jean-Baptiste Salvaing before they returned from work. When Schneider came home, Abballa slit her throat in the living room, with the child present.

The father texted her from the office to say “I’m leaving,” the documents say. There was no response. He was stabbed upon arriving home.

Neighbors called police, and the attacker said he was holding the couple’s 3-year-old hostage, according to the documents. He told a negotiator from a special police unit that he acted because the French government was preventing the faithful from joining the caliphate, and stressed that he had not targeted civilians but representatives of the French state.

Police stormed the home and killed Abballa, and rescued the child. The boy has been raised by family members since.

After more than five years of investigation and multiple arrests, only Aberouz is facing trial. Charges were initially brought against two others but later dropped.

Aberouz, now 30, was arrested a year after the events, when his DNA was found on the victims’ computer.

Aberouz initially disputed connections to IS, before acknowledging that the group corresponded to his convictions but saying he deplored its extremist methods, according to the court documents.

Aberouz was already sentenced to prison in another terrorism case, for his role in a failed gas canister attack near Notre Dame Cathedral in Paris.

In the Magnanville attack, Aberouz maintains that he never went to the police couple’s home or helped in preparing the attack. He said the DNA found in the victims’ home could have been the result of his shaking hands with Abballa or riding in his car in the days before the attack.

Aberouz’ lawyer Vincent Brengarth said he would plead for acquittal. “My client is determined to prove his innocence,” he told AP. “There is no message in which he talks about an attack.”

Police are hoping that the trial sheds light on the preparations for the attack.

A verdict is expected Oct. 10.