Police walk through the re-opened Christmas market on Breitscheidplatz square in Berlin, Germany, December 22, 2016 | EPA/Michael Kappeler Police officers’ homes raided in Berlin attack cover-up probe Officers alleged to have covered up knowledge of Anis Amri’s past.

German authorities raided the homes and offices of five police officers linked to an alleged cover-up of the Berlin Christmas market attacker's past, according to local media.

According to the reports, police were looking for cell phones to verify whether the officials were communicating about the alleged cover-up.

Earlier this month it emerged that Anis Amri, who carried out the deadly attack in Berlin last December, was a known drug dealer and police allegedly had enough evidence to jail him up to six months before the attack in which 12 people died.

Prosecutors had believed that Amri was involved only in petty crime, based on police documents. But another document suggested police had known about his drug trafficking past and after the attack they tried to alter the wording in their files to avoid blame.

Berlin Interior Minister Andreas Geisel said Amri should have been arrested long before he carried out the attack and called for an investigation into the case.

The Social Democrats, far-left and Greens in the regional Berlin parliament agreed to set up a parliamentary investigation committee into the case, with a first report expected on July 3.