Counter-terrorism officials believe that Anis Amri, the Berlin killer, had terrorist accomplices and was likely to have been trying to reach them when he was shot dead by a police officer in Italy.

Amri, who it has emerged pledged allegiance to Isis and its leader Abu Bakr al-Baghdadi before carrying out his attack on a Christmas market in the German capital, made a 1,000-mile journey across Europe through three countries before the fatal encounter in a Milan street in the early hours of the morning.

Tunisian-born Amri was found in the district of Sesto San Giovanni which has a large Muslim population, mainly from North Africa, during what the police described as a routine check.

Security agencies in Italy have now begun to examine the movements and communications of Islamist suspects to search for any links with Amri.

Milan has been connected with Islamist terrorist plots in the recent past. Four people were arrested in April over plots to carry out attacks on the Vatican and the Israeli embassy in Rome. The main suspect, Abderrahim Moutahrrick, was alleged to have received his instructions from an Isis-held area in Syria in the name of al-Baghdadi. A second man, Abderrahmane Khachia, also of Moroccan background was subsequently detained.

The following month, a Pakistani man was arrested in Milan, along with two Afghans in Bari – one of whom was subsequently freed – in an investigation into an alleged terror cell planning to carry out attacks in Italy and London with airports and hotels as potential targets.

Berlin Christmas market lorry attack Show all 18 1 /18 Berlin Christmas market lorry attack Berlin Christmas market lorry attack Several people have been killed after a lorry drove into crowds at a Christmas market in Berlin REUTERS/Fabrizio Bensch Berlin Christmas market lorry attack 'At least nine' people have been killed and more than 50 injured. AP Berlin Christmas market lorry attack Emergency Services rush a Berlin market victim to an ambulance Associated Press Berlin Christmas market lorry attack Police cordoned off the square at Kaiser Wilhelm Memorial Church following the incident REUTERS Berlin Christmas market lorry attack Rescue workers inspect the lorry that crashed into a Christmas market close to the Kaiser Wilhelm memorial church in Berlin EPA Berlin Christmas market lorry attack Emergency crews inspect the lorry that ploughed into a Berlin Christmas market, killing at least nine people AFP Berlin Christmas market lorry attack Fire crews attend the scene of the attack AFP/Getty Berlin Christmas market lorry attack Armed police secure the site of a lorry attack at a Christmas market in Berlin REUTERS Berlin Christmas market lorry attack Crushed debris is visible beneath the wheels of the vehicle REUTERS Berlin Christmas market lorry attack An injured man is pushed to an ambulance REUTERS Berlin Christmas market lorry attack Medics attend an injured person after the lorry attack which killed at least nine and injured more than 50 people AFP/Getty Berlin Christmas market lorry attack Firefighters examine the lorry which was rammed into a Berlin Christmas market REUTERS Berlin Christmas market lorry attack A person is carried into an ambulance REUTERS Berlin Christmas market lorry attack View of the lorry that crashed into a Christmas market in Berlin, killing at least nine and injuring at least 50 people AFP/Getty Berlin Christmas market lorry attack Rescue workers push a person on a stretcher to an ambulance Getty Berlin Christmas market lorry attack Firefighters assess the damage after the lorry rammed the Christmas market, killing 'at least nine', and injuring more than 50 people AP Berlin Christmas market lorry attack Firefighters stand beside a toppled Christmas tree at the site of the suspected terrorist attack in a Berlin Christmas market AP Berlin Christmas market lorry attack Damaged stalls at the scene of the incident at a Berlin Christmas market where at least nine people have been killed EPA

A team of detectives from Berlin has travelled to Milan.

Thomas De Maizière, the German interior minister, said: “This manhunt, which has ended with success, doesn’t end the investigation – we have to investigate further.

"Unfortunately the terror threat has not changed, it is still at high risk.”

Germany’s federal prosecutor, Peter Frank, stressed that the main focus now was on establishing whether Amri had accomplices.

Dashcam footage captures the moment truck crashes into the Berlin Christmas market

He said: “For us it’s important to know whether the person being sought had a network of support or help in preparing and carrying out the attack and also when he fled, whether there were others that knew or gave him help.

"That is now of central importance for us, also to understand his escape route.”

Amri, 24, was regularly in touch in Germany with the Iraqi-born cleric Ahmad Abdulaziz Abdullah, who, preaching under the name of Abu Walaa, has praised Isis and exhorted his followers to join the jihad in Syria.

Abu Walaa was arrested earlier this year, but, according to German security officials, the network he helped set up continues to function.

Angela Merkel reacts to shooting of Berlin market attack suspect

Antonio De Iesu, Milan’s police chief, said Amri was like “a ghost” as he was not carrying any documentation or a mobile telephone.

However, he was carrying a pistol, believed to have been used in the murder of a Polish driver whose truck was used in the Berlin massacre, a small knife and a small amount of money.

Mr De Iesu said his force was investigating what had brought the wanted fugitive to the city, undertaking a journey across, Germany and France.

Amri’s only known Italian connection was to the island of Lampedusa, where he had stayed in a refugee camp, and Sicily where he had served a prison sentence.

Robert Emerson, a security analyst, said: “A lot is being said about security flaws in the Schengen system with Amri getting out of Germany and then getting to two other countries.

"But this wasn’t a journey without risk and we have to ask who may have helped him and why he was so keen to get to Milan.