Kirtley has also pleaded guilty to possession of a firearm during the commission of a crime and destruction of evidence.
The killing goes back to February of 2013. Authorities discovered the body of George Richardson Jr. with multiple gunshot wounds. Kirtley was arrested a short time later.
As part of the deal, prosecutors will no pursue second-degree murder. They are asking the judge to give Kirtley a 15 year prison sentence with 9 years fixed.
Authorities say Kirtley killed Richardson and stole his Jeep Wrangler, which was later found partially underwater in the Snake River a couple miles from Kirtley's home.
Sentencing is set for April 1st.