For years, Germany has been strengthening security measures around Christmas markets in reaction to an attack in 2016 in which a man killed 12 people by driving a truck into a market in central Berlin.

The police have deployed more uniformed and plainclothes officers. They have erected barriers to keep cars and large vehicles away from crowds, set up security cameras and cordoned off large pedestrian-only areas. In some markets, they have enforced stop-and-search protocols. And intelligence services have stepped up their surveillance, often working closely with migration authorities.

Germany also banned knives at Christmas markets this year, after a deadly knife attack at a festival in August. Offenders now face a fine of up to more than $10,400.

Yet an attacker still managed to pierce that vigilance on Friday by driving into a crowd at a Christmas market in the eastern city of Magdeburg, killing at least five people, including a 9-year-old child. The attacker entered the market through an emergency exit before leaving through another one, according to the Magdeburg police. The driver, who the authorities identified only as Taleb A. in keeping with Germany’s privacy laws, was arrested shortly afterwards. He faces charges of murder and attempted murder, the police said on Sunday, after the man was remanded in custody.

“This is going to be a big debate in Germany,” said Peter Neumann, a professor of security studies at King’s College London. “The fact that was possible yesterday shows that something must not have worked.”

Outdoor Christmas markets are a beloved German tradition and tourist attraction, but the large crowds they attract have made them targets.

Although the police do not yet know the motive for the Friday attack, the state interior ministry said the suspect appeared to have been acting alone. The driver, a citizen of Saudi Arabia, had lived in Germany for decades on a visa that allowed him permanent residency.

After the attack, local leaders moved to assure residents that Christmas markets were safe.

The interior minister in the state of Bavaria in southern Germany, Joachim Herrmann, said on social media that the authorities would increase security at Christmas markets.

Yet Professor Neumann said that rather than relying on increased security measures at Christmas markets, the emphasis should be on identifying perpetrators long before they have time to act.

Some 60 to 80 per cent of so-called lone-wolf attackers talk about their plans beforehand, he said. However, the challenge for security forces is deciding who to prioritise monitoring with limited resources.

Nicolas Stockhammer, a professor of security studies at Danube University in Krems, Austria, said that in the future, all Christmas markets need to be protected by automated barriers that do not allow vehicles other than police cars and ambulances to pass. Many cities already have them, including Berlin, which installed additional
automated barriers after the 2016 attack.

New York Times News Service