In 1988, Richard Mason, his son-in-law Kenneth Griffith, and Earl Smock were riding all-terrain vehicles (ATVs) through the backwoods of Signal Mountain near Chattanooga, Tennessee. When the three men did not return home, relatives reported them missing and a search began. Their bodies were subsequently found off Big Fork Road near the community of Suck Creek by a resident, while their ATVs were located down an embankment on the side of Roberts Mill Road.
The land where the men had been riding was owned by Frank Casteel's family. According to accounts described in the case history, Casteel had grown increasingly frustrated with people trespassing on the property. After noticing a rise in intrusions, he consulted a police officer, who advised him to keep a logbook documenting everyone he observed on the land. Multiple witnesses later recalled Casteel making statements about his frustration with trespassers, including that he "would kill if he had to." Following the discovery of the three bodies, Casteel became a suspect.
Casteel was convicted in 1998 of three counts of first-degree murder and was sentenced to life in prison. In 2001, the Tennessee Court of Criminal Appeals overturned the convictions and ordered a new trial because portions of recorded conversations should not have been played to the jury. In 2003, Casteel was retried and again convicted of the three murders, and he returned to prison.
Casteel died in prison in May 2019 at the age of 71.
The case received significant media attention over the years. Unsolved Mysteries aired a segment on the killings in a season 2 episode that first broadcast on January 3, 1990. A&E's City Confidential series covered the case in a season 3 episode titled "Dangerous Trespassing." Investigation Discovery also portrayed the murders in an episode of its series "Bloodlands," titled "Signal Mountain Murders," which aired on August 18, 2014.