A suspect is in custody but police still are looking for the weapon and the motive behind the fatal shooting of a faculty member at the University of North Carolina at Chapel Hill on Monday afternoon.

Neither the victim nor the assailant has been identified after the early afternoon shooting sent the university with more than 30,000 students into lockdown for hours. The suspect was detained about 90 minutes after the gunfire interrupted activities at the school's Caudill Laboratories, a chemistry studies building.

"We want to ensure that we gather every piece of evidence to determine exactly what happened here today and why it happened," UNC Police Chief Brian James said at a news conference Monday evening. "It is too early in this investigation to know a motive for the shooting."

Detectives won't get clues into the motive until they speak with the suspect, he added.

Investigators have not found the firearm that was used in the shooting and it's not known whether it was legally obtained, James said.

No one else was injured, officials said.

"This loss is devastating and the shooting damages the trust and safety that we so often take for granted in our campus community. We will work to rebuild that sense of trust and safety within our community," UNC Chapel Hill Chancellor Kevin Guskiewicz said.

James said it was unclear whether the victim and the assailant knew each other.

"That will hopefully be uncovered through interviews of the suspect as well as any witnesses that may be available," he said.

Classes and campus activities were canceled Monday and Tuesday, officials said. This is the second week of fall semester classes at the flagship university of the 17-member UNC system.

After 911 calls about the shooting came in shortly after 1 p.m., university police issued an alert advising students to go inside immediately, close windows and doors and to wait until further notice, according to an email. A witness on campus told CNN they were locked down in their building and saw armed officers searching campus.

Video from CNN affiliate WRAL showed a large number of police vehicles at the campus with their emergency lights flashing. At times, people walked out of nearby buildings in a single-file line with their arms in the air.

Police detained one person before the suspect's arrest but they determined "very quickly" it was not the gunman, James said.

The suspect was taken into custody shortly after 2:30 p.m., Guskiewicz said. The university continued in lockdown for a couple hours after the suspect was detained because authorities were working to confirm they had the right person and trying to find the firearm that was used, James told reporters.

The university has a student body of about 32,000, along with more than 4,000 faculty and 9,000 staff members.

The FBI is assisting in evidence gathering, officials said.

Forty-nine school shootings have happened in the US this year, including the UNC shooting -- 34 have been reported on K-12 campuses and 15 on university and college campuses -- according to a CNN tally.