A teenage girl was arrested on Thursday for allegedly plotting a mass shooting at her high school on Valentine’s Day.

Trinity Shockley, 18, was arrested for conspiracy to commit murder, intimidation and conspiracy to commit intimidation. She is being held without bond in the Morgan County Jail in Martinsville, Indiana.

According to a probable cause filing submitted to the court, the FBI’s Sandy Hook Promise Say Something Anonymous Reporting System contacted the local sheriff after a tipster said their friend was planning an attack, had access to an AR-15 rifle and had just ordered a bulletproof vest.

It said the tip revealed that the person in question was obsessed with Nikolas Cruz, the mass murderer who opened fire at Marjory Stoneman Douglas High School in Parkland, Florida, on Feb. 14, 2018. He killed 14 students and three staff members.

The tipster described their friend as “Jamie,” a 12th grader who identified as transgender, according to court documents. Snapchat messages sent to the tip line included one where “Jamie” characterized her plans as “Parkland part two,” records showed.

“I’ve been planning this for a YEAR,” she said in one of the cited messages.

Court documents showed that Shockley sought mental health counseling on Tuesday at Mooresville High School, where she was a senior.

She disclosed being sexually attracted to Cruz and said that “she has already named the children” she planned to have with him, according to the documents. They also claimed that she showed the counselor a heart locket necklace with Cruz’s photo inside and said she had written to him several times.

Police executed a search warrant of the apartment Shockley shared with her father on Wednesday, according to official documentation, at which point they discovered on Shockley’s bedroom wall photos of Cruz; Dylan Roof, who killed nine people at a South Carolina church in 2015; and Andrew Blaze, who killed three people at a Pennsylvania grocery store in 2017.

The teen’s backpack was decorated with buttons of the killers’ faces — which also graced the wallpaper of her laptop, officials said. On display in her room was a poster for “Zero Day,” a 2003 film depicting a school shooting, court documents showed, and inside her notebooks were illustrations of swastikas and the words “kill,” “bang” and “I hate you all DIE DIE DIE.”

Her diary entries contained confessions of self-loathing and revelations that she was bullied in school, according to official records. “These thoughts won’t stop. I want to hurt others. All of the time!” the documents showed her writing last month.

As the anonymous tip about “Jamie” suggested, Shockley’s home contained AR-15 magazines, ammunition and a soft armor vest, police said.

Shockley later told investigators that she was “joking” about her plans and said that she did not have access to a gun, court documents revealed; however, Shockley’s cited social media posts contained photos of the magazines, flattering messages about Cruz and Roof, and threats to carry out a school shooting.

The Mooresville Schools district released a statement saying that it was aware of the arrest and that Shockley “will not return to the school.”

Mooresville Police Detective Matthew McDaniel said in court records that Shockley had received mental health counseling since freshman year and had expressed suicidal thoughts in the past but that the school said “nothing was significant enough to cause intervention.”

Her father “would deny her the access to the resources” each time Trinity “would try to receive mental health assistance,” according to information McDaniel said he received from the school.

“It was [the school’s] understanding that Mr. Shockley did not believe in mental health treatment and did not take his daughter’s conditions seriously,” McDaniel said in the probable cause filing, explaining that when Trinity turned 18 last November, she signed up for treatment on her own.

Shockley told investigators she was bullied after a drunk driver struck her in 2022 while she was waiting for the school bus, the documents said.

The incident, according to local media reports, left her with a fractured femur, fractured arm, sprained ACL, two brain contusions and a web compression fracture.

At the time, the school rallied around her and raised more than $12,000 for her recovery.

“They’ve been really responsive,” her aunt Angela Altmeyer told at local reporter at the time. “They’ve been wanting to send cards and whatever they can do.”

ABC News reached out to Trinity Shockley’s father, Tim Shockley, and other family members for comment. No court date has been set.