A woman has pleaded guilty but mentally ill to first-degree murder in the deaths of an elderly couple who were killed in their home in Algonquin in 2020, McHenry County prosecutors said Wednesday.

Arin Fox, 42, faces 40 to 60 years in prison under the plea agreement, while other charges of aggravated battery and possession of a stolen vehicle were dropped, according to the state’s attorney’s office and court records.

Prosecutors alleged that in November 2020, Fox stabbed to death Noreen Gilard, 69, and Leonard Gilard, 73, in their home in the 600 block of Red Coach Lane. Fox was living with the victims at the time of the killings.

After the attack, Fox drove the Gilards’ car to Douglas County in Colorado, where she checked herself into a psychiatric facility the next night, prosecutors said. Fox made statements to third parties acknowledging that she had harmed the victims, who were then discovered after a well-being check.

Fox was extradited back to Illinois where she was subsequently found incompetent to stand trial in 2021, but was deemed restored to fitness in 2022.

A stipulation signed by Fox says all parties agree that Fox had been diagnosed with bipolar disorder and schizophrenia. Guilty but mentally ill indicates that a defendant has mental illness but understands the difference between right and wrong. Fox’s sentencing was set for Dec. 6.