A photo taken Dec. 20 shows authorities inspecting a truck that had sped into a Christmas market in Berlin the previous day, killing 12 and injuring dozens. A new suspect in the case is being detained in Germany. (Odd Andersen/AFP/Getty Images)

German prosecutors said Wednesday that they have detained a Tunisian man who they think may have been involved in last week’s truck attack on a Christmas market in Berlin.

The 40-year-old, who was not identified, was detained in Berlin during a search of his home and business, federal prosecutors said.

The man’s telephone number was saved in the cellphone of Anis Amri, a fellow Tunisian believed to have driven a truck into the market on Dec. 19. Amri, 24, was killed in a shootout with Italian police in a suburb of Milan on Friday.

Of the new suspect, prosecutors said that “further investigations indicate that he may have been involved in the attack.”

Twelve people died and dozens were injured in the attack. The Islamic State has asserted responsibility.

(Jenny Starrs/The Washington Post)

Prosecutors have until Thursday evening to determine whether the case against the new suspect is strong enough for them to seek a formal arrest warrant. That would allow them to keep him in custody pending possible charges.

Investigators are trying to determine whether Amri had a support network in planning and carrying out the attack and in fleeing Berlin. They are also trying to piece together the route he took from Berlin to Milan.

Italian police have said Amri traveled through France, and French authorities said Tuesday that he made a stop in the eastern French city of Lyon.

On Wednesday, Dutch authorities said it appeared that Amri first had fled through the Netherlands, Germany’s western neighbor.

Jirko Patist, a spokesman for the Dutch national prosecutor’s office, said it was “highly likely” that Amri had been in Nijmegen, in the eastern Netherlands, during his journey to Milan.

Camera images recovered in Nijmegen “found someone we think, rather, of whom we say it is highly likely,” is the same person appearing in photos from Lyon in France, Patist told Dutch public broadcaster NOS.

1 of 32 Full Screen Autoplay Close Skip Ad × Photos from the scene of the Berlin Christmas market attack View Photos The suspect in the attack, 24-year-old Anis Amri, was killed in a shootout with police in Milan on Dec. 23. Caption The suspect in the attack, 24-year-old Anis Amri, was killed in a shootout with police in Milan on Dec. 23. Dec. 23, 2016 Italian police officers stand next to the body of Anis Amri, the suspect in the Berlin truck attack, in a suburb of Milan. Reuters Buy Photo Wait 1 second to continue.

A SIM card found on the fugitive after he was shot led authorities to the Netherlands. Amri had no phone with him in Milan, only the loose SIM card, authorities said.

According to Italian police, Amri also had a pocket knife and a few hundred euros in a backpack when officers on a routine patrol stopped him to ask for identification.

He also carried a .22-caliber pistol that he then used to shoot a police officer, hitting him in the shoulder, police said.