ST. JOSEPH, Mo. -- A northwest Missouri teenager has described himself as "spoiled and stupid" while pleading guilty to killing his grandparents.

The St. Joseph News-Press reported 16-year-old Joseph Johnson said he "mistook discipline for abuse" in entering the plea Monday in Buchanan County Circuit Court. According to the plea deal, no other charges, including criminal action, may be filed against Johnson.

Johnson initially was charged as an adult with two counts of first-degree murder. Prosecutors later lowered the charges to second-degree murder.

The teen was home-schooled and lived with his grandparents, 72-year-old James Johnson and 76-year-old Beverly Johnson. They were also his adoptive parents. He was arrested during a traffic stop in July in Platte County a few hours after their deaths. Court records say the deputy who stopped him discovered he had $600, a credit card belonging to his grandparents and directions to Louisville, Kentucky.

Authorities say the couple was fatally shot.

The sentencing is set for March 4.

Information from: St. Joseph News-Press/St. Joe, Missouri, http://www.newspressnow.com