At a news conference on Wednesday, Mr. Geisel raised the possibility that the police were trying to cover up their failure to act on the Nov. 1 document by backdating the Jan. 17 document so that it appeared that the police had conflicting intelligence.
The Nov. 1 document “would have been enough to order an arrest warrant” — and, potentially, jail time, Mr. Geisel said.
Mr. Geisel also said it appeared that officers with the Berlin criminal police had stopped tapping Mr. Amri’s phone in June, despite having permission to monitor it until November.
Germany’s federal interior minister, Thomas de Maizière, who was in Brussels for a meeting with counterparts from other European Union countries, said he was stunned by the revelations, which he acknowledged raised troubling questions.
“I expect all parties involved in the city-state of Berlin to investigate it very thoroughly and very openly now,” he said.
However, Benjamin Jendro, a spokesman for the Berlin police union, told the newspaper Der Tagesspiegel that even if the Nov. 1 warning had been acted on, “There is no guarantee that he would have been arrested.”
Often, in drug trafficking investigations, the priority is finding the people pulling the strings, not the dealers themselves, Mr. Jendro said. “One cannot say that the colleagues have definitely made a mistake,” he continued, and it was impossible to say with certainty that the Christmas market attack could have been prevented.
Mr. Amri, 24, had a long criminal history that included convictions for car…