Sienna Johnson

Sienna Johnson, one of two teenage girls accused of making a violent threat against Mountain Vista High School in 2015, will serve five years in Division of Youth Corrections followed by four years of adult probation, as stated in a plea deal made at a June 7 Douglas County court hearing.

The 17-year-old, wearing her hair tied up and briefly answering District Judge Paul King when called upon, pleaded guilty to conspiracy to commit murder, a juvenile count, and menacing, an adult count. She will serve five years on the conspiracy to commit murder charge - excluding the past 18 months that she has been in custody- followed by four years of supervised probation for the menacing charge. Before her probation begins, she will have drug and alcohol and mental health evaluations.

Johnson will be formally sentenced at a hearing scheduled for Aug. 11.

Johnson and Brooke Higgins were arrested in December 2015 after Text-A-Tip reported their alleged murder plot against Mountain Vista High School. They were sophomores and 16 at the time. Both were charged as adults in January 2016 with conspiracy to commit first-degree murder with extreme indifference and conspiracy to commit first-degree murder after deliberation.

Johnson's sentence is longer than that of Higgins, who was sentenced in February to three years in the Division of Youth Corrections - including the prior year that she was in custody - followed by four years of adult probation. If Higgins successfully completes her probation sentence, she can seal the adult conviction, unlike Johnson. But if Higgins violates her probation, she could face eight to 24 years in prison.

Stipulations of Johnson's probation include monitored access to her computer and electronics, no drugs or alcohol, no contact with Higgins and no possession of weapons. If she violates her probation, she faces two to six years in Department of Corrections.

George Brauchler, district attorney of the 18th Judicial District, said the outcome of both cases is unlike anything he has seen before.

"This is a unique combination," he said. "Maximum supervision possible, maximum accountability that we think we could achieve in court, and also the right opportunity at rehabilitation and correction so that one day they might move on."

According to the arrest affidavit, Higgins brought the idea of a school shooting to Johnson in December 2015 and the two took steps toward carrying out their plan. They planned to kill themselves after carrying out the attack.