The suspect in Berlin’s terrorist attack sent a selfie and the message “pray for me my brother” from inside the truck he is alleged to have steered into a crowded Christmas market, according to German media reports.

Just minutes before the attack, which left 12 people dead and about 50 injured, 24-year-old Tunisian-born Anis Amri sent a message saying: “My brother, everything is all right, God willing, I am in the vehicle now, pray for me my brother, pray for me”.

Amri then sent a selfie from the cabin of the truck, which German media said was fitted with a special locking device designed to automatically stop the lorry in the case of an impact.

“This mechanism has saved lives,” German public television and the daily Sueddeutsche Zeitung quoted government officials as saying, as details of investigators’ probe into last week’s attack emerged.

Berlin police on Wednesday detained a 40-year-old Tunisian man possibly linked to the attack, as investigators try to piece together Amri’s escape route from Germany.

Prosecutors believe the so-far unnamed man could have been a contact point for Amri.

The man’s phone number was stored on Amri’s mobile phone, which was found at the scene of the attack in central Berlin.

Police raided the 40-year-old Tunisian’s Berlin apartment and business, German media reported. Meanwhile Italian police raided several buildings on Wednesday as part of investigations into Amri’s contacts from his time spent in a prison in Italy, according to news agency ANSA.

A policeman light a candle at the makeshift memorial at the Christmas market. Photo: AAP.

Investigators are still attempting to establish how Amri fled Germany after the attack. Days later he was shot dead by Italian police at a railway station north of Milan when he drew a gun on the officers.

Islamic State claims it was behind the Berlin attack and has claimed responsibility for previous terrorist acts in Europe.

Amri was believed to have travelled by train from France to Italy.

However, a Dutch SIM card reportedly found in Amri’s rucksack points to him travelling to Italy via the Netherlands.

Dutch prosecutors say they believe that surveillance footage shows Amri at Nimwegen’s railway station, two days after the Berlin attack.

Both Dutch and German media reported that Amri then took a bus from Nimwegen, near the German border, to the French city of Lyon before travelling on by train to Milan.

A British woman also told Sky News last week that she is convinced she saw Amri at Chamonix, a French resort near the Swiss and Italian borders, two days before he was shot dead in Italy.