A federal lawsuit is expected to be filed alleging the state is responsible for a 23-year-old inmate's death last year.

Carl Sundberg III died in June 2008 while serving time at the Omaha Correctional Center. He had been convicted of felony sexual assault of a child.

His father, Carl Sundberg Jr., alleges the state ignored signs of his son's mental and physical illness.

He says health care providers hired by the state gave his son several doses of medication at once, presumably to take over time. He says they also didn't ensure the drugs were OK to take together.

Sundberg says his son fatally overdosed and/or suffered a reaction from combining drugs.

The lawsuit was expected to be filed Thursday in U.S. District Court.