(CNN) — The three people killed and five critically wounded in a mass shooting at Michigan State University were all students at the university, police said Tuesday morning, as another US community was left reeling after an hourslong manhunt and shelter-in-place orders.

The gunman, who died of an apparent self-inflicted gunshot wound, was identified as 43-year-old Anthony Dwayne McRae, MSU Interim Deputy Police Chief Chris Rozman said. McRae was not affiliated with the university.

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"We have no idea why he came to campus to do this tonight," Rozman said earlier.

The five wounded remain in critical condition, said Dr. Denny Martin of Sparrow Hospital in Lansing. Police have not given victims' names or ages.

The gunman opened fire Monday evening at two campus locations, turning the sprawling university of about 50,000 students into a crime scene and forcing terrified students to run and hide as hundreds of officers in tactical gear swarmed the school -- a now-familiar scene to many US communities.

While the motive remains a mystery, new details about the gunman are emerging:

• A search warrant was executed at a home connected with the suspect, but Rozman would not confirm whether the home was McRae's.

• Police recovered a weapon but have not determined if it was the one used in the mass shooting, Rozman said.

• Shortly after police released McRae's photo, an alert citizen recognized and helped police find him, Rozman said.

The attack came hours before the five-year anniversary of the mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, and marked the 67th mass shooting — with four or more shot, not including a gunman — in 2023, according to data from the Gun Violence Archive.

President Joe Biden was briefed on the Michigan State massacre ahead of a call with Gov. Gretchen Whitmer, according to a White House official.

"This community is struggling to understand why they are the latest in what is a uniquely American experience, and understanding and experiencing a mass shooting in their midst," CNN senior law enforcement analyst Andrew McCabe said.

"The FBI and their colleagues are going through the history of this person to try to understand what his motivations were, to try to understand what brought him to this moment in this community at this time."

But with the gunman dead, the motive behind such inexplicable carnage might never be known.

Slain victims were found in two parts of campus

The first report of shots fired came at 8:18 p.m. ET from Berkey Hall, an academic building on the northern end of campus. Officers responded to the building within minutes and found several shooting victims, including two who died, Rozman said.

Immediately after that, another shooting was reported at the nearby student union building, he said. That's where the third slain victim was found.

As news of the mass shooting spread, anxiety permeated the campus as the gunman remained at large. A shelter-in-place order went into effect, MSU's interim president Teresa Woodruff said.

"One of the things I'm most proud of is, on a campus this size, how quickly every student, staff, faculty member immediately took action," Woodruff said at an overnight news conference. "They sheltered in place, and they did so for hours."

Hours after the first gunshots rang out, the suspect "was contacted by law enforcement off campus," Rozman said. Afterward, it appeared the "suspect has died from a self-inflicted gunshot wound."

MSU students describe terrifying scene on campus

Student Chris Trush saw people running out of the union building -- a congregation spot for students on campus -- shortly before an emergency alert went out to students informing them of the shooting on campus, he told CNN.

Trush had been watching TV just after 8 p.m. in his apartment when he saw police cars and ambulances speeding down Grand River Avenue, he said. Then people started running out of the union building.

"That's when I knew something's really up," he said.

Trush saw dozens of officers begin to swarm the area with long rifles -- and realized a shooting had erupted.

"I'm obviously not going to go outside for the next couple of days," he said.

Another student, Gabe Treutel, and his dorm mates hunkered down during the shelter-in-place order and turned to a local police scanner for information, he said.

Treutel and his friends started barricading their door, just in case a shooter tried to get inside.

Responding to the shooting was a 'monumental task'

Responding to the shooting was a "monumental task" due in part to the size of the campus, MSU Vice President for Public Safety and Chief of Police Marlon Lynch said.

"We have 400 buildings on campus and over 5,300 acres and part of the process of the response that we had is that we were able to divide and organize to be methodical in the search process and obtain evidence and share as it comes through. But with a university our size and the areas that we are responsible for, that becomes a task," Lynch said.

The two buildings at the center of Monday evening's shootings are accessible to the general public during business hours, police said in an early morning news conference Tuesday.

It's not known how long the suspect was on campus before opening fire, police said.

Campus will remain closed

Though officials said there was no longer a threat to the campus, the university will move into emergency operations for the next two days. Students will experience a continued police presence as investigators probe multiple scenes.

All classes, athletics and campus-related activities at MSU are canceled for 48 hours, campus police said. "Please DO NOT come to campus tomorrow," police implored.

All East Lansing Public Schools and city offices also are closed Tuesday because of the shooting.

"Tonight has been horrific. It's been horrific for all of the students here and around the region. Schools have been closed. This has affected our whole region, our whole community. It's affected families, everyone across our community," Lansing Mayor Andy Schor said.

The campus community will need time to heal, officials said.

"This truly has been a nightmare that we are living tonight," Rozman said. "We are relieved to no longer have an active threat on campus, while we realize that there is so much healing that will need to take place after this."

MSU's interim president said such tragedies must stop.

"We want to wrap our warm arms around every family that is touched by this tragedy and give them the peace that passeth understanding in moments like this... we will change over time," Woodruff said. "We cannot allow this to continue to happen again."

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