The president of Tuskegee University in Alabama announced Monday that the school is being closed to outsiders and that its security chief has been fired in the wake of a mass shooting Sunday on campus.

The barrage of gunfire left a teenager dead and injured 16 other people attending an unsanctioned homecoming event, officials said.

Mark Brown, president and CEO of the historically black university, announced the changes as the investigation of the mass shooting continued Monday and the local sheriff warned those responsible for the shooting that "we are going to find you."

"The Tuskegee University community is heartbroken by what happened on our campus Sunday morning," Brown said during a news conference Monday afternoon.

Moving forward, no one will be allowed on the Tuskegee campus without authorized permission or a school-issued identification badge, he said.

"Tuskegee University is no longer an open campus," Brown said. "Effective immediately, we require IDs for everyone to be displayed to enter campus and worn at all times while on campus."

Earlier Monday, the university hired a new campus security leader "and relieved our previous security chief of his duties," Brown said. He did not take questions or elaborate on why the security chief was being replaced.

"Our new campus security chief and ultimately his team will complete a full review, including all implementations of new security procedures," Brown said.

He said Sunday's shooting erupted at the event that was "not approved in advance and in no way was sanctioned by the university."

"Nonetheless, it happened on our campus and we take full responsibility," Brown said.

The deadly barrage of gunfire erupted between 11:30 p.m. Saturday and midnight Sunday in a parking lot that was packed with people on campus to celebrate the university's 100th homecoming, Macon County Sheriff Andre Brunson told ABC News.

The person killed in the shooting was identified as 18-year-old La'Tavion Johnson by the Macon County Coroner's Office. University officials said Johnson was not a Tuskegee University student.

At least 16 other people, including students, were injured during the shooting, including 12 who suffered gunshot wounds, according to police.

Several videos posted on social media and verified by ABC News captured what sounded like automatic gunfire and showed people diving to the ground or taking cover in vehicles.

Brunson said numerous shots were fired during the incident.

"I would say that with the amount of shots that were fired, there's going to be multiple shooters," Brunson said.

The Alabama Law Enforcement Agency, which is leading the investigation, announced Sunday evening that one person had been arrested. Authorities said Jaquez Myrick, 25, of Montgomery, Alabama, was taken into custody while trying to leave the campus after the shooting and faces federal charges of possession of a handgun with a machine gun conversion device.

State police have yet to determine if Myrick was one of the gunmen who opened fire.

No suspect has been charged directly with the shooting.

"I want to say one thing to the people that were shooting: We're going to make sure we find you. We're not going to let them disrupt what we do here in Tuskegee."

Brown said the shooting occurred despite numerous steps the university took before homecoming week to make the festivities safe, including hiring 70 additional law enforcement officers from throughout Alabama and Georgia to help campus and local law enforcement with crowd control.

Brown said efforts were made through social media and advertising to advise visitors that weapons and drugs are prohibited on campus and that visitors could only use clear bags to carry their possessions.

"We did entry checks at all officially sponsored events, some random and some 100% checks," Brown said. "However, the general campus remained open and we did not, nor could we, have planned for security at an event that was not approved in advance or officially sanctioned by the university."

Brunson said he and deputies from his department had been at the campus all day and into the night Saturday, assisting university police and the Tuskegee Police Department with security.

He said he was driving back to the school after taking a break when the shooting occurred.

"First of all, it was just chaotic," Brunson said of what he observed when he arrived at the campus.

He said officers were told an active shooter was held up in a dorm and raced there, running past injured victims, only to learn there was no shooter at the dorm.

"We had to immediately go there. You have to take out the threat first and we found out that it wasn't that case at that time," Brunson said. "As we were running to that dorm, trying to get to the active shooter, we saw people hurt, we saw people laying down, people asking for help. But we had to tell them, we'll be back."

Brown said he eventually went back to help give first aid to injured victims, including those suffering from gunshot wounds.

"Being there and seeing the faces of the students, seeing the anger and the hurt, being afraid and all of that all into one, it was just a horrific scene," Brunson said. "I sympathize with the students because you shouldn’t have seen anything like this."

ABC News' Faith Abubey and Matt Foster contributed to this report.