MARINETTE, Wis. (AP) — A judge has ruled that an 83-year-old man charged with killing a camping couple in a Wisconsin park in 1976 is not mentally competent to stand trial.

During a hearing Thursday in Marinette County court, Judge James Morrison ruled that Raymand Vannieuwenhoven did not understand the proceedings and could not assist in his own defense against two counts of first-degree murder. He ordered the defendant to undergo inpatient treatment and scheduled a status review of the case for June.

Vannieuwenhoven was arrested and charged last year in the long-unsolved fatal shootings of 25-year-old David Schuldes and 24-year-old Ellen Matheys in McClintock Park in Silver Cliff, about 200 miles (320 kilometers) north of Milwaukee.

For decades, the widower and father of five children lived quietly among the 800 residents of Lakewood, a northern Wisconsin town surrounded by forests and small lakes.

At his first court appearance in March 2019, Vannieuwenhoven was asked by a judge if he understood the charges and he answered, “Not guilty, not guilty, not guilty.”

Investigators didn’t have any major leads until 2018, when a DNA lab in Virginia identified the genealogical background of the suspect. Investigators say tests of Vannieuwenhoven’s DNA from a licked envelope matched DNA collected at the crime scene.