Brussels is reeling from an apparent act of anti-Semitic terrorism in the emblematic heart of Europe. As of Sunday morning, four people were dead from a shooting inside the Jewish Museum of Belgium. One suspect is in custody; another is still at large. The brash daylight murders—just hours before Belgians cast their ballots in regional, federal, and European elections Sunday—are being called the first anti-Semitic attack in Brussels since World War II.

Witnesses tell local media they saw an Audi double park on the Rue des Minimes outside the museum, just steps away from a crowded jazz festival, shortly before 4 p.m. local time. A man then stepped out of the car carrying one or two backpacks, entered the museum, and opened fire, apparently randomly. Two women and a man suffered fatal injuries. One witness told RTL television he heard six gunshots followed by a short pause and six more shots. Bystanders report seeing at least one suspect then flee the scene in the Audi. An eyewitness was able to provide the vehicle's license plate number to police.

A spokeswoman for the public prosecutor's office told reporters early Saturday evening in Brussels that one suspect has been apprehended at the wheel of a car matching witnesses' descriptions. According to the spokeswoman, that suspect admitted during questioning to being present at the scene of the crime, but investigators have not yet confirmed the person's role in the shooting. Police are seeking a second suspect who fled on foot and has not yet been identified as they pore over surveillance footage of the area. Authorities are not yet willing to confirm the attack was anti-Semitic in nature.

Witness Alain Sobotik told the Agence France-Presse he saw two bodies in the entrance hall of the museum. "There was a young woman, with blood on her head. She was still holding a brochure in her hands. She appeared to be a tourist," he said. "A little further inside, there was a gentleman sprawled out. A firefighter was palpating his carotid, but I think he was dead."

Belgian Foreign Minister Didier Reynders happened to be in the area at the time of the attacks and heard gunfire. Reynders, who also serves as deputy prime minister, hurried to the scene, saw two bodies, and called paramedics. Forty minutes later, he tweeted, "Shocked by the murders committed at the Jewish museum, I am thinking of the victims I saw on scene and their families."

Jewish community leaders have told local media there had been no threats made against the museum prior to the attack. Belgian Interior Minister Joëlle Milquet at the scene said "everything leads us to believe this is an anti-Semitic attack."

The president of the Committee for the Coordination of Belgium Jewish Organizations (CCOJB), Maurice Sosnowski, told La Libre Belgique, "We are dismayed because we are in the presence of the first anti-Jewish attack in Brussels since the Second World War. It is difficult to think at this point that this wasn't an attack." Sosnowski said Saturday's shooting recalled an anti-Semitic attack two years ago in Toulouse, France.

Then, in March 2012, Al Qaeda-inspired, motorcycle-riding spree-killer Mohamed Merah slaughtered three children and a rabbi outside a Jewish school, days after killing three French soldiers. Merah was gunned down by police after a tense manhunt and violent 32-hour standoff at his apartment. Merah's spree took place a month before France's 2012 presidential election.

Indeed, Belgium votes on Sunday in national federal, regional, and Europe-wide legislative elections. Four hundred million Europeans are eligible to vote across the European Union's 28 countries to elect a new European Parliament.

The run-up to that poll has been marked by uncommonly high support for populist, so-called Euroskeptic parties. High unemployment and sluggish growth across the continent in the wake of European economic and financial crises have spurred hostility toward the euro currency, immigrants, and Brussels itself, which serves as the capital of the EU and home to much of its bureaucracy. But it remains too early to tell whether Saturday's killings are related to the Belgian or European elections.

Meanwhile, Belgian daily Le Soir notes that Saturday's killings come just two weeks after a "European Anti-Zionist Congress" was due to be held in the Brussels suburb of Anderlecht featuring "notorious anti-Semites" as invited speakers. Organized by far-right Belgian parliamentarian Laurent Louis, the congress was ultimately banned by authorities.

In the wake of Saturday's museum murders, Joël Rubinfeld, president of the Belgian League Against Anti-Semitism (LBCA), told AFP, "This, alas, was bound to happen. There is a freeing of anti-Semitic speech. It is the inevitable result of a climate that distills hate."