"I'd like to believe it's the real thing," said Grummer-Strawn, a theology and sociology student from Atlanta. "But you just can't know. That's part of why we're here. It's the pursuit of truth. And it's such a great story."
The university scholars and guest speaker Thomas Allen, author of a 1993 account of the events at the school's former Alexian Brothers Hospital, emphasized that definitive proof that the boy known only as "Robbie" was possessed by malevolent spirits is unattainable. Maybe he instead suffered from mental illness or sexual abuse — or fabricated the entire experience.
Like most of religion's basic tenets, it ultimately comes down to faith.
"If the devil can convince us he does not exist, then half the battle is won," said the Rev. Paul Stark, vice president for mission and ministry at the 195-year-old Catholic school. He opened the discussion with a prayer from the church's exorcism handbook, imploring God to "fill your servants with courage to fight that reprobate dragon."
Some of the non-students in the audience spoke of personal connections to an episode that has enthralled generations of St. Louis residents.
One man described living near the suburban St. Louis home where the 13-year-old boy arrived in the winter of 1949 (his Lutheran mother was a St. Louis native who married a Catholic). Another said she was a distant cousin of Father William Bowdern, who led the exorcism ritual after consulting with the archbishop of St. Louis but remained publicly silent about his experiences — though he did tell Allen it was "the real thing."
Bowdern died in 1983.
Bowdern was assisted by the Rev. Walter Halloran, who unlike his colleague spoke openly with Allen and expressed his skepticism about potential paranormal events before his death a decade ago.
"He talked more about the boy, and how much he suffered, and less about the rite," Allen said. "Here was a scared, confused boy caught up in something he didn't understand.
"He told me, 'I simply don't know,' and that is where I leave it," the author added. "I just don't know."
Allen zealously protects the anonymity of "Robbie," despite others' efforts to track him down to this day.
Gary Mackey, a 59-year-old accountant who left work early to attend the campus event, said he also is unsure whether "The Exorcist" was a work of fiction or instead a riveting real-life account of barely comprehensible forces.
He does know this: He cannot forget the movie that he saw with a buddy four decades ago. They drove 100 miles from their home in Louisville, Ky., to the nearest theater showing it across the state line in Cincinnati.
"I saw the movie when I was 19 years old and it scared me to death," Mackey said. "I think it's the scariest movie ever made."
Blatty, who could not be reached for comment on Wednesday, said in a 2011 interview with The Huffington Post that was timed to the book's 40th anniversary, that the "1949 case was the novel's inspiration." The book and film were set at Georgetown University rather than in the Midwest, and the possessed child became a girl instead of a boy.