LINCOLN, Neb. (AP) — An 80-year-old Nebraska man has been charged with murder after telling police he shot his wife, who had Alzheimer’s disease, because he was struggling to care for her.

Prosecutors upgraded the charges against John Kotopka to first-degree murder on Wednesday — a week after the death of Janet Kotopka, 78. He was originally charged with assault in the June 20 shooting at their home in Lincoln.

Janet Kotopka had been diagnosed with Alzheimer’s disease about two years ago and her health had deteriorated significantly, according to court documents. John Kotopka told investigators he was “exhausted and couldn’t take care of her any longer” and he worried about the potential financial burden of her being cared for at a nursing home.

Kotopka also told police that he started thinking about hurting his wife of 57 years about 10 days before the shooting.

Kotopka is being held in the Lancaster County jail without bond and hasn’t entered a plea. Kotopka’s attorney John Berry said the shooting is a horrible tragedy for the family but he declined to comment on details of the case.