The Michigan State University gunman was found with a note in his pocket indicating a threat to two New Jersey schools, the district’s superintendent said.

Ewing Public Schools closed for the day, but it was later determined there was no threat to the district, Superintendent David Gentile said in a statement based on information from the Ewing Police Department.

The gunman, Anthony McRae, had ties to Ewing Township but has not lived in the area for several years, according to the police statement provided by Gentile.

McRae, who killed three students and wounded five at Michigan State University, was a 43-year-old with a previous gun violation who fatally shot himself after an hours-long manhunt that ended in a confrontation with police miles from campus, officials said.

The residence of Anthony McRae, in Lansing, Michigan. Photo / Carlos Osorio, AP

Investigators were still sorting out why McRae fired inside an academic building and the student union shortly before 8.30pm on Monday. The shootings led to a harrowing campus lockdown and a search for the gunman that ended roughly three hours later.

“We have absolutely no idea what the motive was,” said Chris Rozman, deputy chief of campus police, adding that McRae, of Lansing, was not a student or Michigan State employee.

“This is still fluid,” Rozman said. “There are still crime scenes that are being processed, and we still are in the process of putting together the pieces to try to understand what happened.”

The dead and injured in the gunfire at Berkey Hall and the MSU Union, a popular place to eat and study, were all students, Rozman said. Five remained in critical condition at Sparrow Hospital, said Dr Denny Martin, who fought back tears during a news conference.

“Our Spartan community is reeling today,” Governor Gretchen Whitmer, a Michigan State graduate, said at the briefing.

President Joe Biden pledged his support during a phone call, she said.

“We mourn the loss of beautiful souls and pray for those continuing to fight for their lives ... Another place that is supposed to be about community and togetherness shattered by bullets and bloodshed,” Whitmer said.

A worker cleans up outside Berkey Hall at Michigan State University after three students were shot and killed by Anthony McRae. Police also say five students are in critical condition. Photo / Carlos Osorio, AP

Michigan State has about 50,000 students, including 19,000 who live on the suburban East Lansing campus. As hundreds of officers scoured the campus, about 145km northwest of Detroit, students hid where they could Monday night.

During that time, police released a photo of the suspect, and an “alert citizen” recognised him in the Lansing area, Rozman said.

“That was exactly what we were trying to achieve by releasing that picture. We had no idea where he was at that point,” the deputy chief said.

Police confronted McRae about 8km from campus in an industrial area, where he killed himself, Rozman said.

McRae was on probation for 18 months until May 2021 for possessing a loaded, concealed gun without a permit, according to the state Corrections Department.

In McRae’s Lansing neighbourhood, there was a large police presence overnight. Suzanne Shook said she has lived a block away from McRae for about a year.

“We never spoke to him,” Shook said. “When he would be walking or riding his bike, he was always straightforward and wouldn’t look at anybody.”

Students, meanwhile, recalled the previous night’s terror. Dominik Molotky said he was learning about Cuban history around 8.15pm when he and the other students heard a gunshot outside the classroom. He told ABC’s Good Morning America that a few seconds later, the gunman entered and fired three to four more rounds while the students took cover.

“I was ducking and covering, and the same with the rest of the students. He let off four more rounds and when it went silent for about 30 seconds to a minute, two of my classmates started breaking open a window, and that took about 30 seconds to happen. There was glass everywhere,” Molotky said.

Police investigate the scene of a shooting at Berkey Hall on the campus of Michigan State University. Photo / Al Goldis, AP

“After that, we broke out the window and I climbed out of there, and then I booked it back to my apartment,” he said.

He was unsure whether gunfire hit any of the students.

Claire Papoulias, a sophomore, described on NBC’s Today how she and other students scrambled to escape a history class through a window after the gunman entered from a back door and began firing.

“There was a boy in my class, and he was waiting outside the window, and he was catching people and helping people down,” she said. “As soon as I fell out of the window I kind of hit the ground a little. I just grabbed my backpack and my phone, and I remember I just ran for my life.”

Ryan Kunkel, 22, was attending a class in the Engineering Building when he became aware of the shooting from a university email. Kunkel and about 13 other students turned off the lights and acted like there “was a shooter right outside the door”, he said.

“Nothing came out of anyone’s mouth” for over four hours, he said.

Ted Zimbo said he was walking to his dorm when he encountered a woman with a “ton of blood on her”.

“She told me, ‘Someone came in our classroom and started shooting’,” Zimbo told The Associated Press. “Her hands were completely covered in blood. It was on her pants and her shoes. She said, ‘It’s my friend’s blood’.”

Zimbo said the woman left to find a friend’s car while he returned to his SUV and threw a blanket over himself to hide for three hours.

A worker empties a bucket while cleaning up outside Berkey Hall at Michigan State University. Photo / Carlos Osorio, AP

All classes, sports and other activities were cancelled for 48 hours.

Interim university president Teresa Woodruff said it would be a time “to think and grieve and come together”.

“This Spartan community — this family — will come back together,” Woodruff said.

The shooting came a day before the fifth anniversary of the Parkland, Florida, school shooting that killed 17 and is the latest in what has become a deadly new year in the US.

Dozens of people have died in mass shootings so far in 2023, most notably in California, where 11 people were killed as they welcomed the Lunar New Year at a dance hall popular with older Asian Americans.

In 2022, there were more than 600 mass shootings in the US in which at least four people were killed or wounded, according to the Gun Violence Archive.

- Joey Cappelletti and Mike Householder, AP