There is no evidence to suggest that a teenaged Afghan who injured five people on a commuter train in southern Germany with a knife and axe had ties to an Islamist terrorist network, Bavarian Interior Minister Joachim Hermann said Tuesday.
A hand-painted Islamic State flag and Pashto-language writings found in the Afghan refugee's room - including a goodbye letter to his father and a text calling on Muslims to arm themselves - is evidence suggesting he "radicalized himself," Hermann said during a press conference.
German police shot the 17-year-old dead late Monday following the attack, when he turned on them after fleeing the scene of the crime. Police say they are still investigating whether he was motivated by radical Islam.
Earlier on Tuesday, the Islamic State extremist group claimed responsibility for the attack through the affiliated Aamaq news agency.
The teen was an "Islamic State fighter" and "carried out the operation in response to calls to target states in the coalition fighting Islamic State," the news agency said via its channels on the secure messaging app Telegram.
The teen's stabbing spree with a knife and an axe took place at 9:15 pm (1915 GMT) on a commuter train near the southern German city of Wuerzburg. He reportedly yelled an "Allahu Akbar" (God is great) before being shot dead by police.
The Aamaq claim is typical of the way Islamic State has sought to claim responsibility for recent so-called lone wolf attacks. The claim is phrased in the same way as the group's claim of the truck attack that killed 84 people in southern France last week.
Analysts say Islamic State claims such attackers as members even if they have had no prior contact with the group, as long as they have pledged allegiance to the group's leader, Abu Bakr al-Baghdadi.
Official statements from Germany contradicted the claim of responsibility. Justice Minister Heiko Maas referred to the Afghan as a "lone perpetrator" who had "not coordinated [his actions] with third parties."
Though the teen's motive has not yet been established, similar attacks in Germany have been linked to radical forms of Islam, if not organized networks.
In May, a man allegedly shouted "Allahu Akbar" before killing one person and wounding three at a train station near Munich.
Four of the five victims of Monday's attack were members of a family of tourists from Hong Kong.
The 62-year-old father, his 58-year-old wife, their daughter, 26, and her boyfriend, 30, were injured, while the couple's 17-year-old son escaped unscathed.
Another person sustained minor injuries as the attacker was fleeing the scene, while 14 train passengers suffered from shock.
Three of the victims are still in critical condition, according to the Wuerzburg hospital where they are receiving treatment.
A witness who lives near the location where the train was brought to a halt told dpa the compartment looked "like a slaughterhouse" after the attack.
The Afghan is one of nearly 15,000 unaccompanied minors who applied for asylum in Germany in 2015, according to the BAMF agency for refugees. Many of them suffer from post-traumatic stress disorder.
He came to Germany as an asylum seeker "over a year ago," and lived in a home for young refugees until was placed with a foster family in a town near Wuerzburg two weeks ago, according to Hermann.
"Witnesses have not described him as in any way radicalized or fanatic," Hermann said. "He went to mosques on Muslim holidays but did not seem particularly devout."
German police have also launched an internal investigation into whether shooting him dead was justified, a spokesman said.
Renate Kuenast, a leading politician from Germany's Green Party, has criticized the police's behaviour, saying he should have been incapacitated - not killed.