BERLIN | Tugce Albayrak’s dreams of becoming a high-school teacher came to a brutal end one weekend night last month. The young woman of Turkish descent stepped in to protect two teenage girls from harassment at a McDonald’s in central Germany, enraging the girls’ tormenters.

One of the men allegedly hit the university student in the head in the restaurant’s parking lot. She crumbled to the ground. After two weeks in a coma, her parents took her off life support on her 23rd birthday, ending a short life of promise and courage.

The attack has triggered an outpouring of emotion from a nation that been has been grappling with the integration of immigrants in recent years. People of all backgrounds and ages across Germany have held candlelight vigils, holding heart-shaped balloons, red roses and photos of Albayrak. Hundreds of thousands have signed an online petition demanding she be posthumously awarded a national medal of honor.

German President Joachim Gauck paid tribute to Albayrak as a “role model.”

“Where other people looked away,” Gauck wrote in a weekend letter to Albayrak’s family, “Tugce showed exemplary bravery and civil courage and stood up for victims of violence.”

A surveillance video, published online by Germany’s top-selling Bild newspaper on Monday, for the first time showed details of the fatal attack on Albayrak at 4 a.m. in the town of Offenbach. It shows an apparently enraged man being held back by another young man as he struggles to reach Albayrak.

The poor quality of the nighttime video makes it difficult to make much out. But the man appears to break free and then hit Albayrak on the head. She falls to the ground and stops moving.

An 18-year-old identified only as Sanel M. is in custody over the attack, said Offenbach police spokesman Ingbert Zacharias. He said the Serbian teenager has “been the focus of several police investigations in the past, also in connection with an assault causing bodily harm.”

Offenbach prosecutors’ spokesman Axel Kreutz told The Associated Press that when Sanel M. was picked up shortly after the attack and appeared before a judge, he admitted that he “smacked the victim in the head.” Subsequently, however, he has made no other statements and Krautz said he was not authorized to give out the names of his lawyers.

Police are investigating what led to the assault, and Zacharias said police are still looking for witnesses. The two girls who suffered harassment reported to police over the weekend and have both given statements, Kreutz said. He refused to give any other details about them. Police had previously said they were believed to be between 13 and 16-years-old.

German media have widely reported that Albayrak came to the defense of the two girls as they were being harassed inside the women’s bathroom in the restaurant — a popular late-night hangout. Pictures of the woman with long black hair and dark eyes have been all over television, social media and newspapers in the two weeks since the Nov. 15 attack.

The story has also been closely followed in Turkey, where national newspaper Turkiye on Monday published a story about her with the headline: “Thank you Tugce, we love you.”

Turkish Deputy Prime Minister Bulent Arinc paid tribute to Albayrak after a weekly Cabinet meeting on Monday.

“I wish to God that our daughter Tugce rests in peace,” Arinc said. “She showed great heroism and made a place in the hearts of the German public.”

Thousands of people gathered in Offenbach over the weekend to place candles in front of the hospital where Albayrak died. Similar vigils were held in bigger cities like Berlin and Munich.

Albayrak is expected to be buried on Wednesday if authorities are finished with her autopsy by then, police said. The family has said a public funeral service will be held by an imam and relatives will then carry her body to the cemetery. “I painfully miss my daughter and her smile,” her father Ali told Bild.

Albayrak was a student at Justus-Liebig University in Giessen and wanted to become a high school teacher. On Facebook, she had posted a profile picture of herself in front of a colorfully painted classroom blackboard. Underneath the picture of the smiling petite woman, friends have posted comments in both German and Turkish begging Albayrak to wake up from her coma.

“One day you will stand in front of a black board again and hopefully have your own class in front of you,” one friend posted two days after the attack.

On Sunday, the same friend wrote: “Now you are an angel and you will be with us forever.”

David Rising in Berlin and Suzan Fraser in Ankara contributed to this report.