Tunisian suspect Anis Amri's fingerprints have been found in the cab of the truck that plowed into a Christmas market in Berlin, indicating that he was driving the vehicle, German officials said Thursday.

Authorities across Europe were scrambling to find the 24-year-old suspect, a day after Germany issued a wanted notice for him and warned that he may be "violent and armed."

In Berlin, the Christmas market that was ripped apart by the truck attack reopened, with increased security measures, in a signal of the city's resilience.

German authorities have offered a reward of up to €100,000 (roughly $140,000 Cdn) for information leading to Amri's arrest. Twelve people were killed and 56 wounded in Monday evening's rampage, which was claimed by the Islamic State group.

"We can tell you today that there are additional indications that this suspect is with high probability really the perpetrator," Interior Minister Thomas de Maiziere said after visiting the Federal Criminal Police Office along with Chancellor Angela Merkel.

"Fingerprints were found in the cab, and there are other, additional indications that suggest this," he told reporters. "It is all the more important that the search is successful as soon as possible."

Frauke Koehler, a spokeswoman for federal prosecutors, specified that Amri's fingerprints were found on the driver's door and the side of the vehicle.

"We believe that Anis Amri was steering the truck," she said.

Family asks him to surrender

Investigators searched properties in the western state of North Rhine-Westphalia and Berlin where Amri is believed to have spent time, and also checked a bus in the southwestern city of Heilbronn after receiving a tip, she added. They didn't make any arrests.

In Tunisia, Amri's brothers spoke to The Associated Press, urging him to surrender to authorities.

"Whether he did it or not, I ask him to report to the police. We are suffering because of him," said Abdelkader Amri.

"I hope that it's not my brother and if it was confirmed that it was him, we dissociate ourselves from him and this operation," brother Walid Amri told the AP.

German authorities offered a reward of up to €100,000 for information leading to the arrest of suspect Anis Amri. (Police/Associated Press)

Walid said Amri may have been radicalized in prison in Italy, where he went after leaving Tunisia in the wake of the 2011 Arab Spring uprisings.

Italy's justice ministry confirmed media reports that Amri was repeatedly transferred among Sicilian prisons for bad conduct, with prison records saying he bullied inmates and tried to spark insurrections. He served 3½ years for setting a fire at a refugee center and making threats, among other things — but Italy apparently detected no signs that he was becoming radicalized.

Amri's mother insisted that he had shown no signs of radicalization and questioned whether he was really the market attacker. Speaking Thursday in the central Tunisian town of Oueslatia, Nour El Houda Hassani said poverty drove Amri to steal and to travel illegally to Europe.

'I want the truth to be revealed'

"I want the truth to be revealed about my son," she said. "If he is the perpetrator of the attack, let him assume his responsibilities and I'll renounce him before God. If he didn't do anything, I want my son's rights to be restored."

Tunisian police who interrogated the family on Wednesday took away her telephone and were studying her communications with her son, she said.

German officials put out an arrest warrant for Amri after finding a document belonging to him in the cab of the truck. They say he has used at least six different names and three nationalities in his travels around Europe.

German authorities had deemed Amri, who arrived in the country last year, a potential threat long before the attack this week — and even kept him under covert surveillance for six months this year before halting the operation.

They had been trying to deport him after his asylum application was rejected in July but were unable to do so because he lacked valid identity papers and Tunisia initially denied that he was a citizen.

'Berlin will not change'

The small amusement rides and bright lights displays remained shut off in a sign of continuing mourning for the attack victims at the reopened market. (Sean Gallup/Getty Images)

At the market outside Berlin's Kaiser Wilhelm Memorial Church, police placed concrete blocks at the roadside Thursday to provide extra security as it reopened. In tribute to the victims, organizers decided to do without party music and bright lights and Berliners and visitors laid candles and flowers at the site.

Stall owner Axel Kaiser recalled hearing a "dull bang" and seeing a nearby wooden Christmas market stand smashed to pieces by the truck. He and a friend pulled a woman from the rubble and then he helped tend to dozens of shocked visitors.

"I don't know how she made it out of there. The whole truck must have driven through the stand," he said. "She herself can't remember a thing. She stood up and said she needed a Schnapps."

Still, he said Berliners know there is no such thing as complete security and won't surrender their freedoms.

"Berlin will not change. Berliners won't allow it," Kaiser said. "There's a short pause for reflection, then the Berliner wipes his hands, and life carries on."

"We can't allow these idiots to determine when, where or how we celebrate," he added.

Dalia Elyakim of Israel and 31-year-old Fabrizia Di Lorenzo of Italy were among the 12 killed in the market attack, their countries said, and two Americans were among the wounded.

Berlin's state health ministry raised the number of injured in the attack to 56, saying some victims had reached hospitals on their own.

The agency said 12 people were still being treated for severe injuries, with some still in critical condition. Another 14 people with less serious injuries remained hospitalized and 30 others had been discharged.