MILWAUKEE (WTAQ) - Prosecutors said a man killed a woman in a Milwaukee city park because he thought she was after him – and he believed she had a gun in her purse.

32-year-old James Donegan was charged Thursday with homicide and armed robbery in the death of 45-year-old Teresa Boone.

She was stabbed and strangled on Sunday night at Kilbourn Reservoir Park on Milwaukee’s north side.

A state Justice Department lawyer is prosecuting the case to avoid possible conflicts of interest by the district attorney’s office. That’s because James Donegan is the son of Milwaukee County Circuit Judge Thomas Donegan.

Police quoted the defendant as saying that Boone was following him so, “he took her down” and stole her purse.

Boone is a mother of three who was pursuing a new career in education, and was a student at UW-Milwaukee.

Judge Donegan said his son has mental health problems, and he has not taken his medications lately.

One of the victim’s relatives, Janice Quinn-Mixon, said her family is not ready to believe that mental problems drove Donegan to kill Boone. She said the suspect had the presence of mind to hide Boone’s purse and the murder weapon. And the family wants to know more about Donegan’s mental illness, and why he was not taking his medications.