Alexandre Strens, a young man who was critically injured by gunshot in an attack against the Jewish Museum in Brussels has died of his wounds, a Jewish community leader said Sunday.

Joel Rubinfeld, head of the Belgian League against Anti-Semitism, told AFP that Strens, who was in his early 20s and worked as a receptionist at the museum, died in the afternoon, the fourth fatality after an Israeli couple and a French woman.

The shooting which took place in central Brussels on Saturday afternoon, drew condemnation from European leaders, and was blamed by Israeli Prime Minister Benjamin Netanyahu on a growing wave of anti-Semitism sweeping Europe.

Belgian prosecutors on Sunday said they were looking for a lone suspect in the lethal weekend shooting spree.

Deputy prosecutor Ine Van Wymersch said the suspect “probably acted alone, was armed and well prepared.”

Police had detained one suspect late Saturday but he was soon released and is now considered a witness.

A motive was not yet given, but the government has said it had the hallmarks of an anti-Semitic attack.

“Nobody has claimed this attack. All options are still open,” Van Wymersch said.

The two Israelis killed in the deadly attack were identified late Sunday morning as Tel Aviv residents Mira and Emmanuel Riva, who were on an organized, private walking tour of Brussels when the shooting took place.

Belgian Jewish community leader Maurice Sosnowski said Sunday that the museum was not protected like other Jewish centers in Brussels because it is not exclusively a Jewish community structure, and therefore it was “an easy target.”

“This was a pre-planned attack, it wasn’t something that could be improvised. The victims were shot at the entrance to the museum. It seems that there were one or two shooters; the modus operandi reminds us of the shooting in Toulouse,” he added, referring to the March 2012 attack in which four people were killed by a motorcycle-riding gunman outside a Jewish school in the French city.

The Saturday terror shooting has caused a great deal of worry in the Belgium Jewish community and other communities in Europe, Sosnowski said, and noted that “security has been increased to the highest level at all Jewish centers. The local authorities are putting all efforts into solving this case.”

On Sunday morning, before the weekly cabinet meeting, Prime Minster Benjamin Netanyahu, who had condemned the attack immediately after it occurred on Saturday, noted “the hatred the Jewish people are witnessing in these days.” He praised Pope Francis, who is currently on a visit to Israel and the Palestinian Authority, for his “firm stand against anti-Semitism.”

Pope Francis on Sunday said he was deeply saddened by the deadly shooting attack.

“I am profoundly saddened, my thoughts go out to those who lost their lives in the attack in Brussels,” the 77-year-old pontiff said as he arrived in Israel on the final leg of a three-day Middle East tour.

“I entrust the victims to God,” he said.

It was the first fatal attack on a Jewish center since the early 1980s in Belgium, home to some 40,000 Jews, roughly half of them in Brussels, the remainder in the port city of Antwerp.