Triston M. Arnzen pleaded guilty to two counts of attempted first-degree murder Tuesday, a plea that was accepted by 2nd District Judge Michelle Evans.

Arnzen, 15, of Lewiston, appeared in person at the Nez Perce County Courthouse wearing a green T-shirt and blue jeans with his public defender Lawrence Moran for a change of plea hearing. Arnzen’s case has been in mediation since December when the jury trial was initially scheduled.

Arnzen is charged with two counts of attempted first-degree murder. He was charged after the shooting of George Hamblin Jr., who is Arnzen’s stepfather, and Macayla Hamblin, Arnzen’s stepsister, on Feb. 27, 2022, in the 600 block of Bryden Drive in Lewiston.

Evans asked Arnzen how he pleaded to each of the counts and he replied, “guilty, your honor.” She then went over his rights and to ensure that his plea was “knowingly, voluntarily and intelligently” made. After reviewing the rights and some of the information on the case, Evans asked Arnzen how he formally pleaded to each of the attempted first-degree murder counts and he replied, “guilty, your honor” to both and Evans accepted his plea.

Arnzen’s sentencing will take place Oct. 23. Evans also ordered a pre-sentencing investigation by Oct. 5 to provide more background on Arnzen and the case.

The plea agreement agreed upon during mediation is a rule 11 agreement that makes it binding by the court. If Evans orders a sentence outside the guidelines of Arnzen’s rule 11 agreement, the guilty plea is revoked. Evans advised Arnzen that if that happens and the guilty plea is withdrawn, the case will then go to trial.

Nez Perce County deputy prosecutor Emily Snyder outlined the plea agreement, which includes dismissing a sentencing enhancement because the crime was committed with a firearm. By pleading guilty, according to agreement, Arnzen will serve a fixed sentence of three years, plus 12 years, with the total sentence not to exceed 15 years for one count. For the second count, Arnzen will serve three years incarceration, plus seven years, with the total sentence not to exceed 10 years.

The sentences will also run consecutively, which means one sentence won’t start until the other one has been completed. With the consecutive sentences, Arnzen could serve a minimum of six years to a total of 25 years.

Snyder said that the prosecution is asking for a prison sentence but will let the defense argue for a blended sentence, which means that Arnzen could serve out part of his sentence in Juvenile Detention.

Moran went over the court proceedings that led to the guilty plea and mediation, including ensuring there were no constitutional violations, while discussing Arnzen’s rights and the likely outcome if there would have been a trial.

Chloe Marks was also charged in the case and pleaded guilty in December to attempted first-degree murder for taking part in the shooting of George Hamblin Jr. and was sentenced in March to a fixed sentence of four years with 11 years indeterminate, which will be served in joint custody of the Idaho Department of Correction and Juvenile Detention.

Both Lewiston teenagers, who were 14 when they were charged, were charged as adults.

Brewster may be contacted at kbrewster@lmtribune.com or at (208) 848-2297.