[KHTS] – A man accused in the “mercy killings” of his wife and sister is due back in court July 22, when the court expects to have a preliminary hearing date set.

Lance Holger Anderson, 60, of Canyon Country, is accused of fatally shooting his wife and his sister — both of whom reportedly were suffering from mental illness.

He pleaded not guilty at his preliminary arraignment. At a preliminary hearing, the evidence against Anderson will be presented and a judge will decide if there’s enough to merit a trial.

Bertha Anderson, 68, of Canyon Country, was killed by a single gunshot wound to the head, said Lt. Larry Dietz of the Los Angeles County Coroner’s Office.

The two reportedly lived together at the 26800 block of Claudette Street.

Neighbors reported hearing “two loud booms” the night before Bertha Anderson and Lance Anderson’s sister, Lisa Nave, were found dead in their respective homes.

Anderson was apprehended by Los Angeles Police Department officials near the scene of Nave’s death at a convalescent home in North Hills.

A Derringer pistol, which is suspected to be involved in the crime, was found nearby, and Lance Anderson reportedly was arrested without incident.

Nave was killed the morning Bertha Anderson’s body was discovered, after family members requested a “check the welfare” call at the Canyon Country condominium she shared with Lance Anderson.

A Los Angeles Police Department captain initially referred to the incident as a “mercy killing,” because the victim was not chosen at random, and no other patients inside the convalescent home were injured, according to an LA Times report.

Both Bertha Anderson and Nave were reportedly suffering from serious illness at the time of their deaths.

Detective Ron Duval is handling the investigation for the Sheriff’s Department’s Homicide Bureau. He could not be reached for comment Friday morning.

The case is also being investigated by Los Angeles Angeles Police Department detectives because one of the crimes occurred in their jurisdiction.