Tunisian Anis Amri, 24, is the suspected jihadist attacker who on December 19th ploughed a hijacked truck into a Berlin Christmas market, killing 12 people, including the vehicle's registered driver.
After the attack, Amri went on the run - with stops in the Netherlands and France, police believe - before he was killed in a shootout with Italian police last Friday in the northern city of Milan.
The Berlin rampage was quickly claimed by terror group Isis, which also released a video in which Amri is shown pledging allegiance to Isis chief Abu Bakr al-Baghdadi.
Here is what investigators have pieced together so far about the attack, the escape and Amri's possible accomplices - and the questions that remain unanswered.
Attack and escape
December 19th: Amri overpowers Polish truck driver Lukasz Urban and hijacks his 40-tonne lorry, carrying a load of steel beams, in an industrial zone in northwestern Berlin.
Around 1900 GMT, having sent a final phone message to an unknown supporter, he steers the vehicle through the Breitscheidplatz Christmas market, killing 11 people in the crowd and wounding dozens.
Prosecutors say the truck stopped because an emergency braking system was activated, preventing even more casualties.
Amri escapes, leaving behind Urban's corpse in the passenger seat, bearing a gunshot wound and traces of a struggle, but no stab marks as earlier reported.
An autopsy report is not expected until early January but according to prosecutors Urban, 37, died "shortly before" the market rampage.
Police initially follow a false lead and arrest a Pakistani man who was running to catch a subway train. He is later let go.
December 20th: A day after the attack, police find Amri's wallet with identity papers in the cabin of the truck, where they later also discover Amri's fingerprints. Amri's cellphone is recovered just outside the truck.
December 21st: Police issue a public alert and reward for Amri, warning he is likely armed and dangerous.
Amri somehow gets to Nijmegen, a Dutch city near the German border, then travels by bus to Lyon, France.
December 22nd: Amri heads from Lyon station by rail to the French Alpine town of Chambery and then on to Milan.
December 23rd: At around 0200 GMT, Amri is stopped by two police officers for a routine identity check near Milan's Sesto San Giovanni station.
Amri pulls his pistol and fires, wounding one officer, before the second policeman shoots him dead.
German prosecutors say the Erma weapon that Amri fired in Milan had the same .22 calibre as the bullet used on Urban.
After Amri's death, German federal prosecutor Peter Frank said investigators were trying to determine "whether there was a network of accomplices... in the preparation or the execution of the attack, or the flight of the suspect."
On December 28th, German police detained a 40-year-old Tunisian they believed "could have been involved" after searching his home and work premises.
The man's number had been found saved on Amri's cellphone, they said.
A day later the suspect was released, with federal prosecutors saying he "is not the suspected contact of Anis Amri".
Separately, Tunisia's interior ministry announced last week it had arrested Amri's nephew and two other suspects, aged between 18 and 27, accused of being members of a "terrorist cell" connected to Amri.
It made no direct link between the trio and the Berlin assault.
The ministry said Amri had sent money to his nephew so he could join him in Germany, and had allegedly urged him "to pledge allegiance to Daesh (Isis)".
The unnamed nephew had also claimed Amri was the leader of a jihadist group based in Germany, known as the Abu al-Walaa brigade.
Amri fled Tunisia after the 2011 revolution that started the "Arab Spring", evading a prison term for theft, and headed by boat to Italy.
There he served a four-year sentence for setting fire to a refugee shelter - a prison stint during which he was radicalised, security sources believe.
He arrived in Germany in July 2015, amid the chaos of a mass migrant influx, where he went on to frequently change residence and identities.
He was in contact with the German Salafist and jihadist movement, including Iraqi Ahmad Abdulaziz Abdullah A., also known as Abu Walaa, who was arrested in November as a suspected Isis recruiter.
German police monitored Amri from March to September 2016 for a suspected attack and planned break-ins to buy arms, but dropped the investigation thinking he was mostly a small-time drug dealer.
Amri applied for asylum, which was rejected in June. However, his deportation became bogged down in red tape as Tunisia denied he was a citizen.