Tugce Albayrak stepped in after she heard cries for help coming from the toilet of a fast-food restaurant in Offenbach, near Frankfurt, on the night of Nov.15, German media reported.
One of the men returned later and allegedly hit Albayrak's head with a stone or a bat in the parking lot, the BBC said.Albayrak died on Friday, her 23rd birthday. Her family gave doctors permission to switch off her life support.
Vigils in Albayrak's memory took place across Germany, with about 200 people attending a memorial in Berlin on Sunday.
An online petition calling for her to be awarded the national order for merit posthumously has been signed by more than 130,000 people.
Tributes that poured in on Twitter and Facebook describe Albayrak, a German-Turkish university student who wanted to become a high school teacher, as a "hero."
Bild published the video on its website and appealed for witnesses, including the two girls, to come forward.
The footage shows a man — identified by the newspaper as Sanel M., 18 — being held back by another young man as he appears to want to run in Albayrak's direction. Sanel M. is currently in police custody.
In a letter to Albayrak's family, Germany's president, Joachim Gauck, wrote she "will always remain a role model to us," and that "our entire country mourns with you," Sky News reported.
"Like countless citizens, I am shocked and appalled by this terrible act. Tugce has earned gratitude and respect from us all," he wrote.Offenbach police said Monday that no further witnesses had come forward since the release of the video.
"We are still hoping that the two teenage girls will get in touch with us," police spokesman Ingbert Zacharias told The Associated Press.
He said an autopsy to determine the cause of death would take place Monday.
"I painfully miss my daughter and her smile," Tugce's father, Ali, told Bild. "We hope that her body will be released (by the authorities) Monday, so that we can bury her."
