anis amri, berlin terror attack, berlin christmas attack
Handout pictures released on December 21, 2016 and acquired from the web site of the German Bundeskriminalamt (BKA) Federal Crime Office show suspect Anis Amri searched in relation with the Monday's truck attack on a Christmas market in Berlin.Reuters

A Tunisian man suspected of carrying out the Berlin truck attack that killed 12 people and injured 48 during the week leading to Christmas was investigated for an earlier terror plot as well, a senior German official said. A European arrest warrant was issued on Wednesday for the man. 

Anis Amri, the wanted man, was under covert surveillance by the German police for months before it was called off in September. 

There was an investigation against Amri earlier this year on suspicion of "preparing a serious crime endangering national safety". He was due to be deported earlier this year, according to Ralf Jäger, the interior minister of North Rhine-Westphalia state. 

Amri changed houses repeatedly and lived in various places in Germany, Jägers said. However, since February he lives in Berlin most of the time but had visited North Rhine-Westphalia recently.

Amri is in his early twenties and uses six different aliases, according to German newspapers. He also uses three different nationalities. The reports also said that papers from asylum office were found supposedly belonging to Amri in the truck, which was used to ram into people intentionally on the evening of December 19. Investigators also found documents announcing a stay on his deportation inside the truck. 

Germany's federal prosecutor is offering a reward of up to €100,000 for members of the public who help them locate Amri. A poster has been put up in the country saying the same. He has been described as wearing dark clothing, bright shoes and a white scarf on Monday night. 

"Caution: he could be violent and armed," the notice warned. "A reward of up to €100,000 ($104,000) has been issued for information leading to the suspect's arrest." 

anis amri, berlin terror attack, christmas market berlin attack
Handout wanted poster released on December 21, 2016 and acquired from the web site of the German Bundeskriminalamt (BKA) Federal Crime Office shows suspect Anis Amri searched in relation with the Monday's truck attack on a Christmas market in Berlin. The text reads: 'Terrorism. Attention! The person could be violent and armed. Reward up to 100,000 euro.'Reuters

Germany's security service is under pressure after Amri launched the attack despite being on the radar of multiple intelligence agencies for his alleged ties to the Islamic extremists. 

His identity card was reportedly found under the driver's seat of the truck that rammed into people at the Breitscheidplatz Christmas market. His parents are being questioned by Tunisian authorities. He had arrived in Germany in July 2015 and his asylum request was turned down in July 2016. He had previously been in jail in Italy. 

"This is a suspect, not necessarily the perpetrator," Thomas de Maizière, the interior minister said, after briefing the German parliament's domestic affairs committee. "We are still investigating in all directions."

The police had mistakenly arrested a Pakistani asylum seeker in the aftermath of the attack. The 23-year-old was later released after questioning.