The public university, located in New Britain, is attended by more than 10,000 students.
Reports of a person carrying a sword or a handgun led to a three-hour lockdown at Central Connecticut State University on Monday, but police said no weapons were recovered and there was no threat to the campus.
Three school-age people were taken into custody, and one of them later charged. Police said they were investigating whether the scare may have been set off by somebody wearing a Halloween costume.
"We had no real threat to students or faculty," said Chris Cervoni, chief of the campus police.
The primary suspect, a 21-year-old senior at the school, was charged with breach of peace and was expected to be released on $1,000 bail bond. University officials said he is the son of a geography professor at CCSU.
The university declared a campus emergency at about noon Monday, directing people to stay inside and away from windows on the 182-acre campus south of Hartford. State troopers and police from several nearby cities responded, and SWAT teams swarmed around a 400-student residential building, James Hall, where the suspect had been seen.
Officials said that even if it was a prank, the concern was real, noting the person dressed in camouflage was the subject of several 911 calls.
"In this situation, our prayers were answered," said Jack Miller, the university's president, who noted the FBI was among the agencies that responded. "Certainly there have been many other situations that didn't conclude in this way."
Jordan Governale, a 20-year-old junior from Farmington, said he walked by a man carrying a backpack and with a sword and sheath strapped to his back Monday morning. The man was wearing a mask, camouflage pants, knee pads and a vest resembling body armor, Governale said.
A minute later, he said, he saw police.
"At first I thought it was a Halloween costume. But after I saw the cops I thought it was some sort of threat," he said. "It's pretty scary. It's pretty strange, unexpected."
The lockdown was lifted shortly after 3 p.m. University spokeswoman Janice Palmer said that the students who had been inside James Hall were moved to another building for questioning.
Cervoni said the suspect and the two persons of interest were taken into custody on a fourth-floor hallway of James Hall.
Classes were canceled for the rest of the day at the school, which has more than 12,000 students.
Morgan Podlisny, an 18-year-old freshman who lives in the adjacent Seth North residence hall, said she and her friends watched the situation unfold next door.
"Our whole dorm was freaking out," she said. "At first, there were a lot of cops there rushing in with guns."
Two New Britain schools near the campus were also locked down as a precaution, according to the superintendent's office.