Authorities say an eastern Indiana man told investigators that he fatally shot his father and helped his ailing mother overdose on medication as part of a pact with his parents.

Thirty-three-year-old Brian "Scott" Hartman was arrested Tuesday night on preliminary charges of murder and assisting a suicide. Prosecutors say formal charges are expected later this week. Hartman does not yet have an attorney.

According to a probable cause affidavit, Hartman told investigators that he fatally shot his 53-year-old father, Brian E. Hartman, on Feb. 12, then moved the body to the garage of the family's rural Indiana home. Authorities did not find the body until Tuesday.

The mother, 52-year-old Cheri Hartman, was cremated and her funeral was last week.