Natalie 'Samantha' Rupnow's potential target revealed as survivor's mom details how shooter, 15, wore combat boots and pounded energy drinks

A mother of two students who survived the Wisconsin school shooting has revealed chilling new details about shooter Natalie 'Samantha' Rupnow and who may have been her potential target. 

Rupnow, 15, killed a student, a teacher, and then herself at Abundant Life Christian School in Madison shortly before 11am on Monday. Six others were injured, two were said to be in 'life-threatening' condition.

Lyndsay O'Connor, whose children were at school on the day hell broke lose, shared her fear and dread over how much worse it could have been.

She said that Rupnow walked right past her daughter Mackenzie's classroom despite the door being open on her way to the study hall where she eventually opened fire. 

'Mackenzie said she walked by our door; she went to that room,' O'Connor told Wisconsin Right Now.

O'Connor speculated that the regular study hall teacher, who was not there due to a 'planned absence,' may have been Rupnow's target.

'We don't know if her target was the original teacher or just the kids in the class. She would have had to walk by the door and the door was open.' 

She held the usual teacher in high esteem, someone who had made the study hall a 'comforting place' with her own hand-picked students whom the teacher said needed extra help, according O'Connor.

O'Connor praised the teacher who died, a substitute for the study hall: 'The teacher died protecting her class. Many more lives could have been taken. [Rupnow] sent off multiple rounds.'

Madison Police Chief Shon Barnes has said it is unclear if suspect Natalie Rupnow targeted anyone specifically. 

'Everyone was targeted in this incident. Everyone was put in equal danger.' 

Investigators are examining the digital footprint of Rupnow, as well as looking into verifying a possible manifesto that the 15-year-old may have left behind. 

O'Connor said her daughter MacKenzie was 'weirded out' by Rupnow but had tried to make friends. 

'She was very much to herself. She wore a collared shirt with a tie, jeans, and combat boots,' O'Connor said, describing her style as an 'odd version of preppy, not goth.'

While Rupnow is rumored to have 'mourned for friends' and described herself as a loaner, O'Connor suggested she was 'very isolated' but did have some sort of clique at the school.

'They would wear white shirts and black ties. A weird group. She didn't keep a tidy locker.'

'[Rupnow] pounded energy drinks. Little shots of energy things, and she kept to herself,' she added.

She denied, despite Rupnow's isolation and suggestions by the Madison police chief to the contrary, that the girl faced bullying. 

'I think anyone can take anything as bullying these days, but that is not a typical MO at that school,' she said

O'Connor theorizes that Rupnow 'died a broken girl. She died unheard, and she found solace in a bunch of people who didn't promote goodness.' 

The mother of two - who graduated from the school herself - said she only originally heard of the shooting, which killed two people, from a friend while she was driving.

'You need to call your kids and make sure they're safe. There's an active shooter,' she said.

She claimed to have at one point stood up in the 'packed' basement area and offered up a prayer: 'That's the difference between private and public school.'

Eventually, a phone call from an unknown number turned out to be her son, who was at the church sanctuary the survivors were taken to.

'They were in the church sanctuary and were safe and he had eyes on his sister. At that point, I could stop crying.'

Community members in Wisconsin continued to wrestle with grief and called for change in the aftermath of the shooting.

Several hundred people gathered outside the Wisconsin State Capitol for a vigil Tuesday night to honor those slain at Abundant Life Christian School in Madison the day before, with some passing candles to each other and standing close against the winter chill.

The motive for the shooting appears to be a 'combination of factors,' Madison Police Chief Shon Barnes said Tuesday as he appealed to the public to call in to a tip line and share what they might know about the shooter.

He offered no details about what that motive might be, though he said bullying at Abundant Life Christian School would be investigated. 

He also said police are investigating writings that may have been penned by Rupnow and could shed light on her actions.

'Identifying a motive is our top priority, but at this time it appears that the motive is a combination of factors,' Barnes told reporters.

Two students among the six people wounded Monday remain in critical condition. Officials have declined to disclose the names of the victims.

'Leave them alone,' Mayor Satya Rhodes-Conway said.

Police got a 911 call at 10:57am Monday morning, and within three minutes, county sheriff's deputies had arrived at Abundant Life Christian School, which educates about 420 students. Local police arrived seconds later.

At 11:05am, they said that they'd found the shooter wounded and recovered the weapon. Rupnow was pronounced dead on the way to hospital.

Simultaneously, fire department workers got to the scene and began to care for the victims.

Barnes said police were talking with the shooter´s father and other family members, who were cooperating, and searching the shooter's home.

The shooter's parents, who are divorced, jointly shared custody of their child, but the shooter primarily lived with her 42-year-old father, according to court documents.

Investigators believe the shooter used a 9mm pistol, a law enforcement official told The Associated Press. 

The official spoke on the condition of anonymity because they were not authorized to discuss the ongoing investigation.

The school was just days away from closing for Christmas Vacation and students were gearing up for Monday night's basketball game.