MURFREESBORO, Tenn. -- Investigators confirm they have made an arrest in Thursday's e-mail threat at Middle Tennessee State University. Justin Davis, 19, is a student from the Antioch area of Nashville.

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He was charged with an act of terrorism and three counts of arson, said Kyle Evans, a spokesman for the Murfreesboro Police Department. Davis was jailed on $500,000 bond and did not yet have a lawyer. Evans said no motive had been determined, but said Davis was cooperating with investigators about the case. Authorities believe Davis acted on his own, and no additional arrests are expected.

MTSU officials canceled classes from Thursday at noon until Oct. 15, saying they had received a credible threat. The university's fall break was already scheduled for Oct. 11 to 14.

University President Sidney McPhee sent an e-mail to all faculty, staff and students at the university in Murfreesboro, closing the campus at noon on Thursday.

MTSU spokeswoman Lisa Rollins said an e-mail through Yahoo.com was sent Wednesday to an administrator on the business faculty, threatening large-scale devastation or destruction if classes were not canceled. The e-mail did not mention names or give a method of operation.

Three threatening e-mails had been received since Wednesday evening.

After classes ended Wednesday, an e-mailed threat was more widely circulated. Rollins said the e-mail did not say how people would be harmed.

Rollins said a remodeled residence hall called Miss Mary had been evacuated for a time Wednesday night. She said concern was heightened by the setting of three small fires on campus recently; students were evacuated each time.

However, MTSU Police Chief Buddy Peaster said in a press conference Thursday afternoon, “My understanding is that there was one fire.”

One MTSU student said she was evacuated from the residence hall Lyon Hall three times after seeing smoke twice Wednesday night and once Thursday morning.

“At first, we were just told it was a fire in the kitchen," she said, "but the second two fires, we weren’t told anything.”

About 3,500 students and their family members, in some cases, live in residence halls and apartments on campus. They were not evacuated, but Peaster said that security and presence around the residence halls will be beefed up.

"We have not determined that there is a need at this point to try to evacuate the campus or to evacuate any residence halls," said Peaster on Thursday. “There has not been any individual that we know of at this point that has been pointed out to be the only suspect. There is not someone at this point in time that we have knowledge of as being the victim or a victim in this that is being pinpointed."

In addition to the campus police, Murfreesboro city police and the Tennessee Highway Patrol special operations unit were on campus Thursday. Rollins said other agencies alerted included the FBI, the U.S. Department of Homeland Security and the Tennessee Bureau of Investigation.

Gov. Phil Bredesen released a statement saying the events at MTSU are troubling, and the university's move to cancel classes was warranted. He also commended the steps taken to protect the community.