 -- Anis Amri, a suspect wanted in connection with the Christmas market attack in Berlin, is very likely the assailant, according to German Federal Interior Minister Thomas de Maiziere.

"We can tell you today that there are additional clues that this suspect is, with very high likelihood, the perpetrator," Maiziere told reporters at a press conference Thursday. "Fingerprints in the cab of the truck have been found, and there are also other clues that suggest that [he is the perpetrator]."

Frauke Koehler, a spokeswoman for the German federal prosecutor's office, said Amri's fingerprints were discovered on the steering wheel, on the driver's side door and elsewhere in the cab of the tractor-trailer that was used on Monday to plow into a crowded Christmas market at Breitscheidplatz, a public square in the heart of Berlin. Based on this evidence, prosecutors "assume that Anis Amri was driving the truck" and have issued a warrant for his arrest accordingly, Koehler said at a press conference Thursday.

The Breitscheidplatz attack killed at least 12 people and injured dozens more, including two Americans. Family members confirmed to ABC News that Richard Ramirez of San Benito, Texas, remained in a Berlin hospital Thursday. He is in stable condition after having emergency surgery for injuries sustained in the attack. His partner of 18 years, a German citizen, was killed, family members said.

The other injured American, Russell Schulz, is also from Texas. The church in Austin where he taught for several years issued a statement Thursday on the news of his injury.

"We are shocked to learn that our friend and former colleague Russell Schulz, beloved professor emeritus of Seminary of the Southwest in Austin, was injured in this week's attack in Berlin," said The Very Rev. Cynthia Briggs Kittredge, Dean and President of the Seminary of the Southwest. "Our community is deeply saddened by the violence, grateful that Russell is alive, and mournful for those who were killed and their families. We pray that the peace that is promised by the coming celebration of Christmas will be known throughout the world.”

Amri's mother insisted that he did not show any signs of radicalization and questioned whether he was really the man who attacked the market, The Associated Press reported.

"I want the truth to be revealed about my son," Nour El Houda Hassani told The AP Thursday while speaking in the central Tunisian town of Oueslatia. "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."

Hassani said poverty drove her son to steal and travel illegally to Europe, according to The AP.

Amri's brothers urged him to surrender to authorities.

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

"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," Walid Amri, another brother, told the AP.

A source told ABC News that Amri was known to U.S. intelligence agencies.

German authorities have launched a Europe-wide manhunt for the suspect. According to a wanted notice, Amri, a 24-year-old Tunisian national, went by six different aliases and is considered "violent and armed." Officials are offering a reward of up to 100,000 euros ($105,000) for information leading to his arrest.

German authorities have not said whether Amri is thought to be still in Berlin or Germany.

ISIS claimed responsibility for Monday's assault. The attacker is "a soldier of the Islamic State," according to a statement released by the terrorist group's Amaq News Channel.

The truck's driver was found dead with gunshot wounds in the back of the Polish-owned tractor-trailer used in the attack. No gun was recovered from the scene, suggesting that the weapon may still be with the attacker. The truck was stolen in Poland from a building site, according to police.

Police said the deceased truck driver was a Polish citizen and was not controlling the vehicle when it drove into the market. The man is being counted among the 12 fatalities.

A 23-year-old Pakistani asylum seeker was initially arrested in connection to the attack and then released on Tuesday night because of insufficient evidence, police said.

Ralf Jaeger, the interior minister of the German state of North Rhine–Westphalia, told reporters on Wednesday that Amri had known ties to the local radical Islamic scene and he had been deemed a threat by several security agencies.

Amri served a four-year prison term in Italy for arson on its Mediterranean island of Lampedusa, the closest European Union destination for migrants and refugees embarking from North Africa. He lived in the town of Kleve in North Rhine–Westphalia before moving to Berlin, Germany's capital, in February. His asylum application was rejected in July of this year, but he was not deported to Tunisia because authorities couldn't verify his identity without the proper paperwork, according to Jaeger.

Tunisian authorities told ABC News that they have interviewed Amri's father.

Berlin prosecutors said Amri had been under covert surveillance after a tip earlier this year, but the surveillance ended in September when nothing materialized, according to The Associated Press. The intelligence painted a picture of a criminal involved in drug deals and the occasional bar brawl but not necessarily a terrorist.

Police said they were gathering a criminal case against Amri, and the last time information was exchanged regarding his case was as recently as November.

Police raids took place in the city of Dortmund in North Rhine–Westphalia on Thursday morning, the country's federal prosecutor's office confirmed to ABC News. Amri was reported by local media to have lived there intermittently. Police also conducted searches at the Tackenweide refugee center, where Amri may have spent time, in Emmerich, also in North Rhine–Westphalia. The federal prosecutor's office would not say if police operations were connected to the attack in Berlin. Authorities also searched a bus in Heilbronn in the German state of Baden-Württemberg. No arrests were made in any of Thursday's searches, Koehler said.

A spokesman for Berlin police told ABC News on Thursday that his agency is getting tips on Amri sightings "every hour" and that authorities are acting on most of them. He said he doubts the manhunt will continue much longer, though he noted the suspect could be anywhere in Europe by now.

The Christmas market at Breitscheidplatz reopened Thursday. Concrete barriers were being put up for protection there and in other open markets across the city amid concerns about copycat attacks.

The market was packed at lunchtime on Thursday, with the usual aromas of curry wurst and mulled wine. As Germany's Der Spiegel wrote today, "Berliners apparently react the same way they always react when something is going on: They are completely unimpressed."

ABC News' Andreas Bechmann, Mary Kathryn Burke, Matt Gutman and Devin Villacis contributed to this report.