On January 30, Justin Mohn, a 33-year-old Pennsylvania man, was arrested after murdering and decapitating his father, Michael Mohn, and showing off his head in a gruesome, 14-minute-long YouTube video that has since been taken down.

Denice Mohn, Michael’s wife and Justin’s mother, came home to find her husband’s beheaded body with “a large amount of blood around him,” according to court documents.

This week, Justin appeared at a court hearing on charges of first-degree murder, abuse of a corpse and possessing an instrument of crime with intent in the killing. He wore a grim smirk in his police mugshot.

In the court papers, Middletown Township police and Bucks County detectives reported, “Officers also located the deceased male’s head inside of a plastic bag which was inside of a cooking pot in a first-floor bedroom next to the bathroom.”

The machete that was used in the killing was found by detectives,...