The father of Michigan State University gunman Anthony McRae described his son to police as a loner who never left his room, discounting a note in which McRae claimed to be the leader of 20 killers, officials said Thursday. 

"He pretty much sat in his room most of the time. He ate, went to the bathroom in there, so he pretty much never left his room," Michigan State Police Lt. Rene Gonzalez said at a press conference on Thursday. 

"His father didn’t believe that he had any friends, let alone 20 of them that would help him… So we kind of determined that he was the lone shooter in this."

McRae, 43, opened fire inside an academic hall and the student union at 8:18 p.m. on Monday evening, leaving three undergraduate students dead and five others wounded. 

Michigan State University shooter Anthony McRae

This booking photo provided by Michigan Department of Corrections shows Anthony McRae. (Michigan Department of Corrections/AP)

He turned the gun on himself as police made contact with him about 3.8 miles off-campus after an hours-long manhunt. 

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McRae was carrying one 9mm handgun and had another 9mm handgun in his backpack. Police also found eight loaded magazines in his backpack, two empty magazines, and a two-page note in his wallet that contained threats to businesses, schools in New Jersey, and a church. 

"It appears, based on the content of the note, that he felt that he was slighted in some way by people or businesses," MSU Police Chief Chris Rozman said Thursday. 

"Did a mental health issue amplify that, or was it a component of that? We’re not sure at this point. I just want to assure everybody that that’s the question on all of our minds, and we’re working our best to try to determine that as best as possible."

McRae legally purchased both handguns that he used in the shooting, but never registered them. He was arrested in 2019 for carrying a concealed weapon without a license, a felony that would have prohibited him from owning a gun if he was convicted. 

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The Ingham County Prosecutor's Office dropped that felony charge and McRae pleaded guilty to a lesser misdemeanor count of possession of a loaded firearm in a vehicle, which did not impact his ability to own a gun. He was sentenced to 18 months of probation in that case. 

All three students who were killed in the shooting were undergraduates from the suburbs of Detroit. The university identified them as Alexandria Verner, a junior from Clawson; Arielle Anderson, a sophomore from Grosse Pointe; and Brian Fraser, a sophomore also from Grosse Point. 

MSU victims

Arielle Anderson, a sophomore from Grosse Pointe; Alexandria Verner, a junior from Clawson; and Brian Fraser, a sophomore also from Grosse Point, were killed in the attack.  (Fox News)

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Five others were critically wounded and transferred to Sparrow Hospital for treatment. One of the wounded students was upgraded to stable condition on Thursday.