A young Afghan who attacked passengers on a train in Bavaria with an axe had entered Germany last summer with a wave of migrants, officials said on Tuesday, raising more questions about Chancellor Angela Merkel's open-door refugee policy.
The 17-year-old, who a witness said shouted "Allahu Akbar" (God is Great) during the attack, severely wounded four Hong Kong residents on the train late on Monday, then injured a local woman after fleeing, before police shot him dead.
The case is likely to deepen worries about so-called "lone wolf" attacks in Europe and could put political pressure on Merkel, who has welcomed hundreds of thousands of migrants to Germany over the past year.
The attacker came to Germany as an unaccompanied minor and was registered as a refugee on June 30 last year in Passau, officials said. Germany welcomed about 1 million migrants in 2015, many fleeing war in Afghanistan, Syria and Iraq.
"In the minds of many people, his arrival is directly linked to Merkel and her liberal refugee policies," said Frank Decker, political scientist at Bonn University.
The attack took place days after a Tunisian delivery man plowed a truck into crowds of Bastille Day revelers in the southern French city of Nice, killing 84. Islamic State has also claimed responsibility for that incident.
Public support for Merkel has risen since Britain voted on June 23 to leave the European Union, helping reverse a fall in her popularity caused by the refugee crisis. Decker said a Nice-style attack here could quickly end those gains.
"It would boost those who have called Merkel's policies a mistake," he said. "Merkel would be blamed."
Unlike neighbors France and Belgium, Germany has not been the victim of a major attack by Islamic militants in recent years, although security officials say they have thwarted a large number of plots.
A leader of the anti-immigrant Alternative for Germany (AfD) said Merkel and her supporters were to blame for the dangerous security situation because their "welcoming policies had brought too many young, uneducated and radical Muslim men to Germany".
Imam Arbab Ahmad, whose mosque in Wuerzburg lies about 12 kilometers (7.5 miles) from the scene of the attack, said he feared a backlash against Muslims after the attack.
"I am anxious," he said. "It was a totally inhumane attack on innocent people. Every human being should condemn it, not just Muslims."
Police found a hand-painted Islamic State flag in the refugee's room at his foster family's home, along with a letter he appeared to have written to his father, which officials said read: "And now pray for me that I can get revenge on these non-believers, pray for me that I go to heaven."