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The alert had been issued Wednesday night.
Monmouth University lifted a shelter-in-place order after an investigation into a "possible armed subject" found that a curling iron "was mistaken for a weapon," a university official said.
Police at Monmouth, in West Long Branch, New Jersey, had received a report at 9:15 p.m. Wednesday of a "possible armed subject" on campus, the school said in an alert posted to its website.
Multiple local and county law enforcement agencies searched and secured the campus, the university said.
"Detectives were able to utilize video footage and other technology based on the description provided and identified a person of interest, a currently enrolled student," Patrick F. Leahy, the president, said in a letter posted early Thursday.
He added, "Based on interviews with that person, law enforcement personnel were able to determine that the person was in possession of a curling iron that was mistaken for a weapon."
The university issued an all-clear notification a short time later.
"All clear-the shelter in place on campus has been lifted, the campus is safe, an elevated police presence remains," school officials said on Twitter early Thursday. "Additional information will be sent via email."
All classes before noon on Thursday have been canceled, the school said.
ABC News' Robinson Perez, Ahmad Hemingway and Kevin Shalvey contributed to this report.