Originally Published: 14 FEB 23 04:01 ET

Updated: 14 FEB 23 16:14 ET

By Holly Yan, Caroll Alvarado, Amanda Watts, Michelle Watson and Nouran Salahieh, CNN

(CNN) -- The gunman who killed three Michigan State University students and left five others in critical condition may have had plans to target two schools in New Jersey, police there said.

Anthony Dwayne McRae, 43 -- who had no known ties to the university -- opened fire Monday evening on two parts of campus, MSU police said. He was later found dead from an apparent self-inflicted gunshot wound.

When McRae was found by police in Michigan, "he had a note in his pocket that indicated a threat to two Ewing Public Schools," the police department in New Jersey said Tuesday. MSU police confirmed McRae had a note, and Ewing police said local schools no longer faced a threat.

Like many scenes of carnage at US schools, the deadly rampage at Michigan State forced students to jump out windows and run for their lives. Claire Papoulias was in history class when "all of sudden I heard gunshots directly behind me," the sophomore told CNN on Tuesday.

"The shooter opened the back classroom door and started firing at my classmates in the back, wounding them. I smelled and saw the gunpowder," Papoulias said. "I thought I was going to die."

When the gunman stepped out of the classroom -- leaving the door wide open -- some students bravely smashed a window and helped others jump out of the first-floor classroom, Papoulias said.

"There was a boy on the other side of the window catching people who were jumping out the window. He stood there and risked his life to catch people," Papoulias said.

"My feet hit the ground running. I forgot everything I owned because that didn't matter. I was focused on making it out alive. I jumped out the window and I ran as fast as I could."

'Everything you'd want a student to be'

University police identified the slain students as junior Arielle Anderson, sophomore Brian Fraser and junior Alexandria Verner.

Anderson and Fraser graduated in 2021 from high schools in Grosse Pointe, school superintendent Jon Dean said at a news conference.

None of the five victims hospitalized in critical condition have been publicly identified.

When Clawson Public Schools Superintendent Billy Shellenbarger learned of Verner's death, he described her fondly.

"She's everything you'd want a student to be. She's everything you'd want in a friend, sister," he said.

"Her kindness was on display every single second you were around her," said Shellenbarger, who is friends with Verner's family.

Verner graduated from Clawson High School, where she excelled in academics, volleyball, basketball and softball, Shellenbarger said. She also thrived in many leadership groups at the school.

"If you knew her, you loved her," Shellenbarger wrote in a letter to Clawson families, "and we will forever remember the lasting impact she has had on all of us."

'I am filled with rage ... about our children being killed'

While the campus of 50,000 students grieves those slain and wounded, investigators are trying to figure out what prompted the bloodshed.

"We have no idea why he came to campus to do this," MSU Interim Deputy Police Chief Chris Rozman said hours after the shooting.

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

There have been 12 school shootings so far this year, according to a CNN tally. The shooting at Michigan State marks the first at a college or university this year.

Michigan is still grappling with the November 2021 mass shooting at Oxford High School that left four students dead and six others injured.

"As a representative of Oxford, Michigan, I cannot believe that I'm here again doing this 15 months later," US Rep. Elissa Slotkin said at a Tuesday news conference about the MSU mass shooting.

"And I am filled with rage that we have to have another press conference to talk about our children being killed in their schools."

There are children in Michigan "who are living through their second school shooting in under a year and a half," Slotkin said. "If this is not a wake-up call to do something, I don't know what is."

"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."

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

• McRae had "local ties to Ewing Township" in New Jersey but had not lived there in several years, Ewing police said. While it's not clear why McRae might have planned to target schools in New Jersey, Ewing police said the"investigation revealed that McRae had a history of mental health issues" but did not elaborate.

• 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 whether 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.

• McRae had had to forfeit a weapon and was sentenced to a year of probation after he was arrested in June 2019 by Lansing police and charged with a felony for carrying a concealed weapon without a permit, Ingham County court and state criminal records show. He pleaded guilty to a misdemeanor for possession of a loaded firearm in a vehicle and was discharged from probation in May 2021, court records show.

The FBI and university police are asking "anyone with photos or video surrounding the active shooter incident or the suspect" in the MSU massacre to submit their material, the FBI's Detroit office tweeted.

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."

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 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.

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."

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, university 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.

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 see 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.

"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."