Teen pleads guilty to triple murder of girl and parents after he was caught in bed with her then went on run

Mauricio Johnson pleads guilty to murdering Shelly Moon, her mother Margarett Moon and her mother’s boyfriend Nikki Metcalf

Mauricio Johnson in his mugshot after being arrested in February for triple murder (Tooele County Sheriff’s Office)

A teenager has pleaded guilty to the triple murder of a 16-year-old girl and her parents after he shot the victims dead then went on the run when he was caught in bed with the girl.

Mauricio Johnson pleaded guilty on Tuesday to three counts of first-degree murder and admitted to three special allegations of using a firearm in the killings of Shelly Moon, her mother Margarett Moon and her mother’s boyfriend Nikki Metcalf back in February, according to the Humboldt County District Attorney’s Office.

Johnson, who was 18 at the time of the killings, had been hanging out with 16-year-old Shelly and a group of other teenagers at her home on the Native American Bear River Band of the Rohnerville Rancheria Reservation in Humboldt County, California, on the night of 9 February.

Two of Shelly’s siblings who were unharmed in the attack detailed how the attack unfolded in an arrest warrant, previously obtained by Mercury News.

According to the warrant, Ms Moon came home to find the group drinking alcohol and was upset by the situation.

The other teenagers, who were Shelly’s cousins, left the home around 4am but Johnson stayed behind.

Soon after, Mr Metcalf walked into Shelly’s bedroom and found Johnson on top of Shelly on her bed, the documents state.

Mr Metcalf hit Johnson, who then walked out of the room pulling up his pants and took a gun out of his backpack, the documents say.

Johnson shot Mr Metcalf once in the head, killing him.

The teen then shot and killed Ms Moon and Shelly, later telling investigators he killed them because “he did not want to have any witnesses”.

Police were called to the bloodbath around 8am the following morning when Shelly’s 13-year-old sister called 911 to report her three family member “bleeding out”.

Shelly Moon was shot dead by Johnson because he said he “didn’t want any witnesses" (Facebook)

Shelly and Mr Metcalf were pronounced dead at the scene while Ms Moon died in hospital.

Meanwhile, in the hours between the murders and the 911 call, the killer had gone on the run.

Johnson’s brother Damon Johnson told police he came home covered in blood and “in a panic” and told him he “had shot someone”.

Johnson later admitted to his brother that he had shot multiple people after Mr Metcalf “got tough” with him, the warrant states.

Mr Johnson’s girlfriend also told police her boyfriend’s brother was crying and told them “I wasn’t thinking”.

At this point, the 18-year-old then fled in a car with his mother’s boyfriend Von Keener, authorities said.

His mother Melissa Johnson also allegedly fled in a separate car.

Police tracked down the fugitive to Utah on February 11, locating the two cars driving together through Tooele County.

Shelly’s mother Margarett Moon and her boyfriend Nikki Metcalf were both killed in the bloodbath (Facebook)

Authorities said they believe the two cars were communicating with each other using two-way radios and were using the scanner to avoid law enforcement.

Ms Johnson pulled over in her vehicle without incident while her son and boyfriend allegedly failed to stop and were detained when officers spiked their car’s tyres.

Johnson was then extradited to California to face the murder charges.

Johnson reached the plea deal this week to sentence him to 150 years to life in prison rather than going to trial where he could have received life in prison without the possibility of parole.

The DA’s office said it agreed to the deal because of several factors including that Johnson was aged 18 at the time of the crime so there is the possibility that he could undergo “positive transformation” behind bars.

As a youthful offender, the deal means he could be up for parole in 25 years.

“Attorneys and victim advocates from the District Attorney’s Office spoke with many members of the victims’ families, friends, and additional members of the community,” the DA’s Office said in a statement.

“Understandably, given the terrible harm done by the defendant, the people most affected by the murders expressed differing views on whether to accept the plea or proceed to trial.”