It was clear Friday why prosecutors took Sienna Johnson’s plans to commit murder at her high school so seriously – her own words in dozens of pages of her own journals and recorded police interviews reveal a teen seemingly committed to murdering classmates and her family.

Throughout her journals, analyzed by 9Wants to Know, Johnson plotted to “blow up” her school and contemplated killing her family. She wrote about meeting her schoolmate and co-conspirator, Brooke Higgins, and of their plans to acquire guns to cause a massacre that would “lock my place in history forever.”

BACKGROUND | Teen accused of planning high school attack could spend 5 years in prison

“Do you think we should be taking this stuff seriously?” a Douglas County detective asked Johnson during a recorded interview.

“Should we be taking your journal seriously?”

Johnson replied: “In a way because there was a point in time where it was more of a fantasy, but then when I really started to think about it I got more invested. When I meet Brooke it became really real to me.”

In her journal, Johnson described meeting Brooke Higgins as a kind of relief, saying at one point, she was grateful she would no longer have to work alone.

“I have finally met the perfect person!” Johnson writes. “Someone who is as angry as me, hates humankind as much as me, and someone who’s got what it takes to bring vista (sic) down. We are about to make this school a living (expletive) nightmare. God, Brooke and I will be unstoppable.”

These images are taken directly from Miller's diary. (Photo: Provided to 9Wants To Know)

She explained to detectives in a recording why she thinks Higgins was drawn to her.

“Someone told Brooke, I was an evil (expletive) or something like that and then Brooke asked me like ‘let's shoot up the school, like I’m not joking’ and I was down because I was like planning that for a few months,” Johnson told the detective.

Her journal entries indicate that Johnson had been considering, and more seriously acting, on her plan to “blow up” Mountain Vista High School, by describing her attempts to build explosives and apparently searching for different weapons online.

When the detective asked Johnson if she and Higgins meant to go through with their plans in December, she said that they didn’t think it would be possible.

“We decided together that we weren’t going to be ready until next year,” Johnson said, indicating they were having trouble acquiring weapons. “Our main thing was like getting guns I guess.”

In a journal entry, dated 12/9/2015, Johnson wrote: “We found someone who will hook us up with guns and we’re trying to decide what we are gonna get.”

In a separate entry, Johnson compiled a list, along with numbers that are presumably prices of different weapons she appeared to be seeking out, including a website where guns are sold.

She continues the 12/9/2015 entry saying they’ve found someone who can help get guns and plan on purchasing a pistol.

“For the moment, we’ve decided to get a pistol with an extending clip,” the entry reads, in part. “Speaking of guns, I got my daisy powerline 304 airsoft gun today! We plan on practicing target shooting with BBs at coyote skate park during our off period on Thursday.”

These images are taken directly from Miller's diary. (Photo: Provided to 9Wants To Know)

The journal entries show that Johnson had been plotting a mass murder independently of Higgins, and considered a variety of means to complete the killing. In an entry dated 10/15/15, Johnson wrote: “Tonight, I showed my first sign of interest in actually proceeding to go through with this massacre that “will lock my place in history forever” I can’t wait!!! I’m making my first little homemade bomb not really a bomb, more like a toy or prank. I don’t care I’m just trying to get something to explode as a first test/experiment.”

She told detectives that she was inspired by Columbine, and started considering a school shooting in September.

Johnson told the detectives that she didn’t “see a point in life” and that she looked at the Columbine shooters as idols.

“Back in September (of 2015) I started getting a really strong hate for my family and everyone around me because I felt like I wasn’t taken seriously and I felt like I wasn’t heard and I felt like everything was just a joke to everyone,” Johnson said.

“I started watching lots of documentaries about Columbine and that really inspired it to be honest,” she said. “I think of them as Gods.”

Authorities were alerted to the girls’ plans from an anonymous tip and Johnson was placed on a mental health hold at Children’s Hospital in December 2015. She described to the police that she “faked her progress” for the first few days of getting treatment, but ultimately, she confessed to the plot.

“I felt like I should just come clean and be honest and everything because like I just don’t want to live this way anymore,” Johnson said.

In her journals, she not only wrote about the conspiracy to kill her classmates and her family, she also wrote about hurting herself, and her desire to die. While the journal entries show detailed plans to kill many people and her attempts to complete that goal, they also describe a teenager in deep pain.

All of that was apparently important to Senior Chief Deputy Jason Siers, who prosecuted the case. In a statement sent to 9NEWS, Siers said, “This agreement strikes the balance of making sure the community is safe but not throwing away the key on Sienna.”

In court on Friday, Johnson promised the Douglas County district judge that she would not get into trouble again. She’s expected to serve up to five years in a youth detention facility and will face four years of supervised probation upon her release.