Brian Laundrie's family attorney, Steve Bertolino, released a notebook found near his body, which has Laundrie's admission of killing Gabby Petito.

In the notebook, one short sentence caught everyone's attention as it reads, "I ended her life."

The notebook, initially obtained by Fox, contains Brian's reasoning for killing 22-year-old Gabby.

It says that the killing was "merciful," as Petito allegedly was injured and in pain.

An attorney for the Petito family, Patrick Reilly, called Laundrie's claims "nonsense."

In his notebook, Brian, 23, wrote that the couple suffered "an unexpected tragedy" after Gabby slipped in a freezing creek in Utah. The note says:

"I found her breathing heavily, gasping my name, she was freezing cold."

"The temperature had dropped to freezing, and she was soaking wet. I carried her as far as I could down the stream towards the car, stumbling exhausted in shock when my knees buckled, and I knew I couldn't safely carry her."

"I started a fire and spooned her as close to the heat, she was so thin, had already been freezing too long."

Brian continued writing before taking his own life:

"She had a small bump on her forehead that eventually got larger. Her feet hurt, her wrist hurt, but she was freezing, shaking violently, while carrying her, she continually made sounds of pain, laying next to her, she said little lapsing between violent shakes, gasping in pain, begging for an end to her pain."

"She would fall asleep, and I would shake her awake, fearing she shouldn't close her eyes if she had a concussion. She would wake in pain, start the whole painful cycle again while furious that I was the one waking her."

"I don't know the extent of Gabby's injuries. Only that she was in extreme pain."

Brian's confession states:

"I ended her life, I thought it was merciful, that it is what she wanted, but I see now all the mistakes I made. I panicked, I was in shock. But from the moment I decided, took away her pain, I knew I couldn't go on without her."

"I'm sorry for everyone's loss. Please do not make life harder for my family, they lost a son and a daughter. The most wonderful girl in the world. Gabby I'm sorry."

The note ends:

"I have killed myself by this creek in the hopes that animals may tear me apart. That it may make some of her family happy. Please pick up all of my things. Gabby hated people who litter."

Petito and Laundrie traveled across the country in the summer of 2021. He returned to their Florida home without her on September 1. Brian went missing even before her body was found.

His body was found in October, a month after Gabby's. The cause of Petito's death was homicide by strangulation.

Bertolino said he wanted to "share with the public the note that the FBI alluded to when they said on January 21, 2022, that Brian claimed responsibility for the death of Gabby Petito."

The Petito family attorney Patrick Reilly slammed the note, "He is writing a letter as though he wants people to feel sorry for him."

The Lifetime movie, The Gabby Petito Story, is in the making.