A Hutchinson teenager charged as an adult with setting a fire that killed his mother and sister has declined to take a plea deal.

The attorney for 16-year-old Samuel Vonachen says he will pursue a defense of mental disease or defect.

The Hutchinson News reports prosecutors offered to allow Vonachen to plead guilty to first-degree murder and drop other charges. Vonachen’s attorney, John Henderson, said his client would not accept the deal.

Vonachen’s 47-year-old mother, Karla Jo Vonachen, and his 11-year-old sister, Audrey, died in the fire in September 2013. His father escaped the burning home.

The trial was scheduled to begin Sept. 21 but it was continued. No new date was set.