Teen killer wrote chilling note in her journal right after brutal murder of 9-year-old girl

This article contains graphic details which some readers may find distressing.

A terrifying diary entry a 15-year-old wrote just after she murdered a little girl ended up being key to getting her to confess to the chilling crime.

On October 21, 2009, nine-year-old Elizabeth Olten was on her way home from a friend's house in St. Martins, Missouri, when she bumped into Alyssa Bustamante.

Elizabeth had promised her mom that she would be home in time for dinner, but after encountering the teen, she never made it.

Alyssa Bustamante murdered nine-year-old Elizabeth Olten in cold blood. (MySpace)

Bustamante lured her into the woods where she strangled her, stabbed her and then slit her throat, before burning her body and dumping her in a shallow grave.

On the same night, Elizabeth's mom Patty Preiss formed a search party to look for her, and cops tracked her phone to a nearby woods located between her house and her killer's.

Police interviewed the Bustamante family, after it was revealed the youngest daughter was playing with Elizabeth that night.

While searching the house they found Bustamante's diary admitting to the murder, and what she wrote inside was harrowing, to say the least.

Bustamante pleaded guilty to second-degree murder. (Department of Corrections)

It read: "I just f**king killed someone. I strangled them and slit their throat and stabbed them now they're dead. I don't know how to feel atm.

"It was ahmazing. As soon as you get over the 'ohmygawd, I can't do this' feeling, it's pretty enjoyable. I'm kinda nervous and shaky though right now. Kay, I gotta go to church now... lol."

Bustamante was later seen confessing to the murder during a police interrogation after law enforcement told her they had the diaries.

It is understood that Bustamante was taking antidepressants at the time and had spent 10 days in a mental health facility prior to the murder taking place.

In 2012, Elizabeth's mom Preiss took Pathways Behavioral Healthcare to court alleging the clinic ignored 'well-documented violent proof' when they made the decision to allow her to leave.

Bustamante pleaded guilty to second-degree murder and armed criminal action, and was sentenced to life in prison. Just last month she was denied parole.

Bustamante is locked up in Chillicothe Correctional Center in Chillicothe, Missouri, US.