Tristan Dilley, 14, was found dead in her bed on Sunday by her younger brother

Fourteen-year-old Tristan Dilley seemed to have everything to look forward to.

The vivacious teen was a freshman at Silsbee High School in Silsbee, Texas, and a valued member of their cheerleading squad. She participated in the school’s first homecoming pep rally late last month and, on Saturday night, attended a school dance and sleepover at a friend’s house.

But on Sunday night, authorities say, Tristan’s 13-year-old brother discovered her dead in her second-floor bedroom at her mother’s home in Buna, Texas. She had been shot twice in the head with a .22-caliber magnum revolver two days before her 15th birthday.

Her brother found her body, clothed, in a large pool of blood on top of the bed. She wasn’t facing her killer when she died.

“She never saw it coming,” Jasper County, Texas, Sheriff’s Lt. Ryan Cunningham tells PEOPLE. “You could tell from the scene there was not a struggle or a fight. She was comfortable with knowing the person.”

As investigators would come to discover, Tristan’s suspected killer, an older teen, was someone she knew — though their relationship was kept partially secret from both of their families.

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Tristan Dilley
| Credit: GoFundMe

The Case Is Cracked as Loved Ones Grieve

Lt. Cunningham, who worked alongside Jasper County Sheriff Mitch Newman and Lts. Scotty Duncan, Jason McClelland and Cal Morgan, says detectives quickly ruled out a break-in in connection with Tristan’s death.

“She was very positive,” Silsbee High School Principal Paul Trevino tells PEOPLE. “She had that type of personality that people wanted to be around her and hang out with her.”

“It’s difficult for me to think of a student being in fear or in pain as their last experience,” her English teacher told the Beaumont Enterprise.

In her obituary, Tristan was remembered as an athletic student and “a very kind, sweet and compassionate young lady who was loved by so many. She will be greatly missed by all who knew her.”

An online fundraiser was launched to help pay for her funeral, which is scheduled for Saturday.

Investigators learned that she had been dating a boy named “Adam,” Cunningham says — but neither her family nor her fellow cheerleaders knew much about him, other than his name and what they believed was his age: 16 years old.

Her dad told authorities that Adam was “tall and lanky” and “supposed to be a high school basketball player,” Cunningham says.

School records and officials were no more successful in locating Tristan’s boyfriend, but investigators caught a break when they began searching through her phone and Facebook activity, which pointed to his true identity: Paul Audrey Adams, a 19-year-old nursing student at Lamar State College, less than an hour away.

Some of the messages between Tristan and Adams showed they were planning to meet at her mom’s house on Sunday, the day she died, Cunningham says.

Tristan, who stayed with friends the night before, was home alone while her mom ran errands and her body was found shortly after 7 p.m. According to Cunningham, authorities believe she was killed sometime after 3:30 p.m.

Her mother had gone to check on her in her bedroom after returning home that evening, but Tristan didn’t respond from her bed and, with the lights off, her mom assumed she was sleeping after her busy Saturday.

When Tristan’s younger brother was sent back upstairs to get her for dinner, he turned on the lights and saw her dead.

Mounting Suspicions

After obtaining evidence of a relationship between Tristan and Adams, investigators started looking for him themselves.

“I called dispatch and had them start pinging his cellphone,” Cunningham says. “We put out a BOLO out for him in the surrounding area. We were able to get a general location of the cellphone and we learned of his address,” in nearby Vidor, Texas.

Authorities arrived there about 1:30 a.m. on Monday, but he wasn’t home. His mother said he’d left the afternoon before, about 3:30, to meet “some girl in Beaumont he met at school,” Cunningham says.

“Both kids were deceiving the parents,” he says. “He [Adams] knew he was too old to be seeing the child.”

Law enforcement searched his room and found a spent .22-caliber magazine casing lying in the middle of his bedroom floor.

“We don’t know if it was from something previous, but we knew it was probably the type of round used [to kill] Tristan,” Cunningham says. “We don’t know if maybe that it was a trophy-type thing. Sometimes they keep memories.”

Paul Audrey Adams
| Credit: Paul Adams/Facebook

A Grisly End to the Search

At 10:30 a.m. Monday, detectives got a call from a Texas Ranger who told them he had gone back to interview Adams’ mother and was talking to her when Adams called her, Cunningham says.

“The Ranger listened for a few minutes and took the phone,” he says. “He tried to get Paul to come in and speak to us, but he didn’t want to come in.”

Cunningham alleges that, in that phone conversation, Adams admitted to the Ranger that he had been over at Tristan’s house the day she died when they heard an intruder coming upstairs.

“He gave a description of an older white male with a beard,” Cunningham says. “He said he hid in the shower and he could hear Tristan screaming, ‘Get off of me.’

“He said he heard two gunshots and heard the man running out of the house. He waited a couple of minutes and then found Tristan dead and he didn’t know what else to do, so he ran.”

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After Adams told the Ranger this story, the Ranger then “heard a distinct gunshot and he believed Paul had shot himself,” Cunningham says.

He says they started searching for Adams when they came upon a tent and his white ’94 Toyota around noon on Monday, next to a canal just east of Vidor.

They were about 150 yards away from the vehicle and continuing to approach when they saw Adams — and saw him reach for a gun.

“As soon as me and my partner said, ‘I think he has a gun,’ we observed the suspect shoot himself in the head and collapse,” Cunningham says.

‘He Knew We Were Coming’

At the scene, authorities discovered a suicide note reiterating Adams’ claims of innocence, which Cunningham says is disproved by the evidence.

“It [the note] was basically verbatim what he told the Ranger,” Cunningham says. “In the letter he said there was nothing he could do to change what happened to her and going to prison wouldn’t be worth it. He said, ‘I know people are going to think I did this.’ ”

But Cunningham says detectives learned that a few days before Tristan’s killing, Adams bought an axe, a machete, a hatchet, several knives, 32 meal rations, cases of water, burlap sacks, dumbbells and duct tape. He had also purchased several sets of handcuffs and chains.

“It was a premeditated event,” Cunningham says.

Detectives also discovered that Adams had downloaded apps from his phone and had been listening to police dispatch traffic as they investigated Tristan’s death, according to Cunningham.

“I think he knew we were coming,” he says, “but I don’t think he realized it was going to be quite so fast.”

With his story of a violent intruder, Cunningham says, Adams was just trying to cast blame elsewhere: “Why would you not immediately notify law enforcement? Why would you run and go to the extent of buying all of these items? It was pretty clear-cut. You could read between the lines.”

Still, even with what authorities now know, it remains unclear how and when Tristan and Adams first met — or what motivated him to kill her.

“It was senseless, and it makes no sense,” Cunningham says. “There are so many questions we can’t answer. We will never know what was going on in his mind and what was said between them.”