The Afghan teenager who attacked and injured four tourists on a train in Germany on Monday evening filmed a video pledging his allegiance to ISIS, according to a news service affiliated with the militant group.
The two-minute video was posted online on Tuesday, hours after the group claimed that the attack had been carried out by an ISIS "soldier," according to SITE Intelligence Group, which monitors jihadist websites.
Earlier on Tuesday, German investigators said a hand-painted ISIS flag was found in the bedroom of the 17-year-old.
The assailant, a refugee, was shot dead by passing special response officers as he fled the train after he attacked passengers onboard the train in Wurzburg, on Monday evening at around 9.15 p.m. Two of the victims were seriously injured.
Bavaria's state Interior Minister Joachim Herrmann confirmed the flag had been found in the teenager's room in Ochsenfurt, but said the teen had acted alone, and that it was too early to say whether he had an extremist Islamic background.
"When we searched through his apartment where is lived at last, we have found a handwritten ISIS flag," he told German news broadcaster ZDF on Tuesday. "We are pursuing every piece of evidence," he continued.
In later comments, the minister said that a note, discovered on the train in the attacker's possessions, indicated he may have been self-radicalized. The minister also noted that people who had known the quiet and calm teen could not understand his actions.
Amaq, a news service closely associated with ISIS's leadership, claimed the group was behind the attack on Tuesday. It said the teen was a "soldier" for the group who was "carrying out ISIS's calls."
Later on Tuesday, Amaq released a video of the purported assailant, identifying him as Mohammed Riyad, according to the SITE Intelligence Group, which monitors jihadist activity.
"I'm a soldier of the Caliphate... ISIS will attack you everywhere...in your villages, cities, and airports," he said in the video.
German investigators, at least so far, have not connected the assailant to ISIS.
The teenager came to Germany as an unaccompanied minor roughly two years ago and had been living in a foster home with a local family in Ochsenfurt since March. Investigators are talking to the family.
Roughly 30,000 Afghans sought refuge in Germany last year alone. Afghanistan remains the second-largest source of refugees in the world, according to the UNHCR. Some 2.7 million Afghans were categorized as displaced last year.
Following the attack, an eyewitness told the Bild newspaper: "I have never seen so much blood before in my entire life."
The special forces unit who shot dead the assailant happened to be in the area at the time on a separate assignment, and intervened when the assailant fled the train after a passenger pulled the emergency stop.
A 62-year-old man and a 31-year-old man were in critical condition after the attack, and two women, aged 27 and 58 years old, were seriously hurt but are expected to survive. All were tourists from Hong Kong, the South China Morning Post reported.
The city's chief executive, Leung Chun-ying, condemned the attack, and said in a statement he would dispatch a team to help the group, believed to be from the same family.
Another woman was hurt as the teenager fled the train, the BBC reported. 14 people are receiving psychological care after they witnessed the attack.
The attack on the train between the German towns of Treuchtlingen and Würzburg, comes only a few days after an attack in Nice – claimed by Isis – killed 84 people, among them at least 10 children.