Leo Frank was murdered 100 years ago Monday in the only known lynching of an American Jew.

A group of 25 armed men broke into the Georgia State Prison in Milledgeville on Aug. 16, 1915, where they kidnapped Frank -- who had been convicted on shaky evidence of murdering a teenage girl who worked at the factory he managed.

Mary Phagan, a 13-year-old who left home three years earlier to find work, was found strangled in the basement of the National Pencil Company -- where she had gone on Confederate Memorial Day 1913 to pick up her paycheck.

Frank, who was born in Texas but educated in the North, was quickly identified as a suspect and convicted despite the key witness for the prosecution -- a black janitor at the factory -- repeatedly changing his testimony and even admitting he made up parts of his story.

Defense attorneys also relied on prejudice to make their case, arguing that janitor John "Conley is a plain, beastly, drunken, filthy, lying n****r with a spreading nose through which probably tons of cocaine have probably been sniffed."

But ultimately, the dynamics in the rapidly industrializing South, where workers came to resent their Northerner employers, spelled doom for Frank -- who was sentenced to death.

“He was the ultimate New York Jew, living in the South, and that brought out a lot of anti-Semitism,” said Mark Moskowitz of the Anti-Defamation League. “People had pretty much convicted him before the trial even began.”

Gov. John M. Slaton later commuted Frank's sentence to life in prison after the factory foreman lost his final appeal to the U.S. Supreme Court in April 1915.

An armed mob calling itself the Knights of Mary Phagan broke into the prison and was allowed to take Frank back to Marietta, near Phagan's hometown, and lynched him at midnight Aug. 17, 1915, before a cheering crowd in an oak grove where the city's iconic Big Chicken now stands.

“It was a festival -- almost like a Roman coliseum," said Catherine Lewis, a history professor at Kennesaw State history professor.

The atmosphere was standard for lynchings, historians said.

“People would show up; they would bring children to witness the lynching,” said Richard Banz, executive director of the Southern Museum of Civil War and Locomotive History. “No one’s covering their face, no one’s ashamed to be a part of this. They want to be seen.”

The incident helped birth two groups fighting on opposite sides of the fight for equality.

The Anti-Defamation League, formed just two years earlier, vaulted to national prominence speaking out against Frank's murder. The Knights of Mary Phagan met atop Stone Mountain in the fall of 1915 and set a giant wooden cross ablaze, reforming themselves as the new Ku Klux Klan.

“Many white supremacists will actually have that etched as a tattoo on some of their bodies,” Moskowitz said. “The white supremacist movement sees Leo Frank as a win for them -- even today.”

Frank was pardoned in 1986, but a Marietta rabbi has asked Gov. Nathan Deal to clear Frank's name in the girl's strangling.

“How hard could it be for the governor or the Georgia House to get behind a resolution saying, ‘In the light of historical research, it is fair to assume that Leo Frank was innocent of all charges,’” said Rabbi Steven Lebow of the Temple Kol Emeth. “How hard could that be? For Leo Frank, and for all of us, justice is the day.”