Mark Warfel, 90, allegedly murdered a young woman. Meanwhile, the suspect has dementia.

WeGoViral Cold Case:

Does the 90-year-old know nothing more about his murder?

For 34 years, Tracy Kroh has disappeared off the face of the earth.

Tracy Kroh disappeared 34 years ago. The cold case is unsolved so far.

The police of Pennsylvania are sure: The then 17-year-old was murdered. Officers consider Mark Warfel, an urgent suspect. Problem: The man is 90 years old and demented, according to media reports.

Earlier this week, authorities targeted Warfel's property in Halifax, a town of 800 residents. The house, shed, and trailer was "systematically demolished," according to a police news release.

The goal is to "bring this investigation to a conclusion and close the Kroh case," a spokesman said. The family of the 90-year-old had cooperated fully.

Pennsylvania police have turned over this property - to no avail.

However: the measures remained so far unsuccessful. Although two corpse-sniffing dogs were also used, the police had to announce on Thursday (local time) that no human remains were found. One would close the property, however, still some days. After that, further excavations may be undertaken.

Mark Warfel has served in the Dauphin County jail since 2019 for several offenses, including burglary and assaulting a nurse.

The missing woman was last seen alive around 10 p.m. on Aug. 5, 1989. At that time, she had been visiting her half-sister, who is the biological daughter of Mark Warfel, at a trailer park in Halifax. Although less than 10 miles from her Millersburg home, the teen never returned home.

Investigators found Kroh's car just a day later, the car sitting intact in Millersburg. Then, four years later, the 17-year-old's wallet was found several miles outside town. It was the young woman's last sign of life.

Questioning 90-year-old Mark Warfel is no longer possible due to his dementia. And so the suspected killer could take the mystery of Tracy Kroh's disappearance to his grave.