Image The police detained a man on Saturday in Brussels after stopping and searching a car with French license plates. Credit... Virginia Mayo/Associated Press

The lawyer, Carine Couquelet, said her client, Hamza Attouh, told the police that Mr. Abdeslam “seemed to be in a very bad state, very nervous, very anxious.” Mr. Attouh said they did not discuss the attacks, according to the lawyer. But he said he told the police that Mr. Abdeslam was wearing a big jacket “with something underneath.” While he did not know what it was, the lawyer said, the sight of it “made him scared.”

Mr. Abdeslam, whose brother died in Paris when he detonated a suicide vest, was stopped by French police officers on Nov. 14 during a routine traffic check as he drove with two friends back to Brussels a few hours after the Paris attacks. But he was allowed to keep going and has since vanished. His two friends have both been arrested.

Mr. Abdeslam is now the target of an intensive manhunt and he has managed to avoid arrest.

A police hotline for information about his whereabouts has received hundreds of calls but none have provided the authorities with enough information to establish his whereabouts. The Belgian news media has speculated that he may be dead.

The Abdeslam brothers both lived in Molenbeek, where they got to know Abdelhamid Abaaoud, an Islamic State militant who is believed to have been the chief planner of the Paris attacks and who died in a police raid just north of the French capital on Wednesday.

The Belgian federal prosecutor’s office said on Saturday that the search of the Molenbeek residence of an unnamed man arrested on Thursday in another Brussels district had uncovered weapons, but no explosives. The arrested person has been charged with “participation in terrorist attacks and participation in the activities of a terrorist organization,” a federal magistrate, Eric Van der Sijpt, said.