By Rick Lyman

New York Times

WEIMAR, Germany >> Residents of Weimar flocked to the German city’s central park to escape unusually scorching heat this week, setting up picnics and watching bees skitter across the wildflowers near a placid reflecting pool.

But for two Syrians also soaking up the sun, who recently arrived in this eastern city of 65,000, the summer idyll belied deeper worries after news of an attack on a passenger train by a fellow refugee.

“When you hear about something like this, like this attack, you are naturally just a little afraid,” said Hanan Alderzy, 28, who arrived in Weimar three months ago from the central Syrian town of Masyaf. “Will people treat you differently?”

She said she understood the fears of her new German neighbors. But, she added, it would be wrong to blame the actions of one refugee on all refugees. “A man must be known by his name, not where he came from,” she said.

It is unclear how fully Germans are prepared to embrace such advice after the episode Monday evening, when a 17-year-old attacked passengers bound for Wurzberg with an ax and knife, wounding five, two critically, before being killed himself by the police.

After hundreds of sexual assaults on New Year’s Eve in Cologne apparently involving male migrants from North Africa, Germany was convulsed over whether such ugly cultural clashes would become standard fare in a country that accepted more than 800,000 asylum seekers last year from the Middle East and elsewhere.

Now, the concern is that this apparent lone-wolf attack on strangers riding an obscure regional train could inspire a fresh round of second-guessing about whether Germany had made a fatal error in accepting so many immigrants.

“It was only one lonely person who did this,” said Heiko Clajus, who was also in the park and who works on a series of memorial projects at the site of the former Buchenwald concentration camp on the outskirts of Weimar.

“You can’t really pin this on refugees in general and say, ‘Oh, all refugees are responsible and must be feared,’” he said. “But it is troubling that we had such an incident in Germany.”

The young attacker on the train has not been identified by officials, but he was widely named in the German media as Riaz Khan Ahmadzai.

On Wednesday, Germany’s federal police said they had confirmed the authenticity of a video attributed to him by the Islamic State, which called him one of its soldiers.

“The foster family were able to identify it, that he had filed it in the room in their home where he had lived, in that they recognized the background,” Joachim Herrmann, interior minister for the state of Bavaria, said Wednesday. “We are absolutely sure, the video is authentic.”

The assessment supports the idea that the teenager had been radicalized quickly; he only moved in with the family several weeks ago.

Thomas de Maizière, Germany’s interior minister, spoke of the attacker as having been “incited” by Islamic State propaganda. But he played down the significance of the video, describing it as being similar to a normal suicide video.

“This is perhaps a case that falls into the gray zone between a rampage and an act of terror,” de Maizière said.

Before this week, the young man had shown no signs of violence. He arrived in Germany last year as an unaccompanied minor, saying he was from Afghanistan, although officials now say he may have been from Pakistan.

He had appeared to be integrating well, having been placed in foster care rather than in a group home. But apparently, after news of the death of a close friend back home last week, he became disturbed and rapidly radicalized, German officials said.

Like cities across Germany, Weimar, famous as the center of Germany’s literary golden age, home to Goethe and Schiller, has had to accept its allotted batch of refugees — about 900 of them in Weimar’s case.

One of them, Lemar Poya, 25, from Afghanistan, lounged on a blanket in the shade at the park, munching on a platter of picnic food prepared by Syrian women.

Poya said he worried that some of the Germans he had met in the months he had been in Weimar would now see him differently.

“I was very sad, and concerned,” he said about his feelings upon hearing of the attack. “Will all Afghans be blamed? I hope not. All I want is to learn the German language and to get work and make a life here.”

While acknowledging that a terrorism-related episode was possible — perhaps likely — many Germans had consoled themselves that, before Monday, there had been none of the type of violence that has hit France and Belgium.

They saw it as a consequence of Germany being more welcoming and integrating than those countries. Now, though, they are not so sure.

“I am really sad right now, because I thought Germany wouldn’t be the target of such attacks anytime soon, because Germany has tried so hard to help the refugees,” said Micha Ott, a graphic designer. “Now, I hope it won’t get harder for the refugees.”

“But,” he added, “we have to face the fact that with this happening here in Germany, the Germans are frightened now.”