The initiator of the investigation was made by the Senate of Berlin. The report says that the police missed a series of opportunities to arrest and deport a Tunisian Anise Amri, who had organized the attack.
It has long been known that Amri adhere to Islamist views, is a security risk, the report said. The police could arrest him on charges related to the distribution and use of drugs, even before December 19, when the attack occurred.
The day he entered the territory of the lively Christmas market on the square Breitscheidplatz, crushed to death 12 people and causing severe injury and maiming dozens of others.
Escaped from the crime scene Amri was killed in a shootout with police in Italy four days later.
Presenting the report, former Prosecutor Bruno Jost told that there had been gross errors that were not supposed to happen.
He noted that although the Berlin police received a signal about the amry as potentially dangerous Islamists prone to violence, surveillance was conducted only on working days.
Observation and stopped after a few weeks, when the police decided that the 24-year-old Tunisian is only a petty drug dealer.
According to Jost, Amri could detain on charges of drug trafficking, but because of the lack of coordination with the Prosecutor's office, he was able to get away with it.
"We cannot say with mathematical certainty that Amri could have been arrested and isolated, but if all worked as needed, that would be a real opportunity to hold him and to leave under arrest for some time," he said.
"Amri was one of those suspects, who was regularly mentioned at meetings of the joint anti-terrorist response center. It was talked about often, perhaps, than about anyone else. And it is impossible then to take and act like it's just some petty thief," added Yost.
The investigation also found traces of fraud in police documents allegedly taken to cover up the blunders of law enforcement.
German police have not publicly commented on the outcome of the investigation.