Belgian police officers stand guard outside the Palace of Justice in Brussels at the trial of Mehdi Nemmouche and Nacer Bendrer. Photo: Reuters / Francois Lenoir.

Police in Belgium are investigating a burglary at the offices of one of the lawyers involved in the trial of Mehdi Nemmouche, the French Islamist who fought with ISIS in Syria, who is accused of carrying out the deadly terrorist attack at the Jewish Museum in Brussels in May 2014.

Lawyer Vincent Lurquin arrived at his office in the Belgian capital on Wednesday to find that a laptop and an extensive file on Nemmouche had been taken from his desk and replaced with threatening signs — a baseball bat and a replica Kalashnikov rifle. A statement later in the day from the Brussels federal prosecutor said that an investigation had been “immediately opened  for burglary and threats using symbols.”

Four people — an Israeli tourist couple, a French museum volunteer and a Belgian receptionist — were murdered in the attack four and a half years ago. The trial of Nemmouche and co-defendant Nacer Bendrer, who is accused of supplying the weapons used in the atrocity, began earlier this month. Among those that have already given evidence against Nemmouche is Vincent Lurquin’s client — an 81-year-old Chilean artist who had just arrived at the Jewish Museum when the attack began.

The artist, Clara Billeke Villalobos, shared her testimony with the court on Jan. 18. She recalled that she had gone to the museum with a friend who had designed one of the exhibitions on display, and that the pair had arranged to have dinner later on with Alexander Strens — the museum employee killed in the attack.

“We heard very loud shots,” Villalobos testified. “I am always apprehensive when I hear gunshots because, in my country, Chile, I escaped dictatorship. I cannot hear gunshots without thinking about death.” She said that she took cover in the basement of the museum, and did not emerge until 10 p.m., more than six hours after the first shots were fired.

“I cannot understand an act like this, why someone thinks he has the right to impose death on others,” an emotional Villalobos continued, as she told the court that her life had been turned “upside down” by the experience.

Lurquin was adamant that the trial would continue, despite the threats he received.

“We will continue the trial and I hope that the jury will understand this,” Lurquin said on RTBF television on Wednesday. “We will continue to help them judge without hatred, without fear, and we will not yield to blackmail.”