Nearly four years after a California family vanished, their remains were found buried in the desert. Who would brutally murder the entire McStay family?

In the Oxygen series "Killer Motive," the dark and twisted motivations behind some of the most shocking murders ever committed are revealed.

Eric Williams also allegedly planned to shoot a judge with a crossbow, blow out his guts with homemade napalm and bury him in his flower bed, Williams’ wife testified in court.

Ashton Matheny is now raising Haisley Jo, who was cut from her mother, Savanna Greywind, in a brutal attack by Brooke Crews in 2017.

Family of Veronica Navarro lamented that they didn’t uncover Joe Carr’s long history of abuse — including killing puppies — before he murdered her.

Murder is an unthinkable act for most, but its roots lie in human emotions, according to former profiler Cliff Van Zandt and psychologist Dr. Peter Morrall. The FBI says that serial killers’ motives are a whole different ballgame, though.

Among typical motives for murder — lust, greed, hatred — so-called "gay panic" has also been used to explain lethal actions in the past. Is it still used in the courtroom?

Get ready for Oxygen's second season of "Killer Motive" with these four unbelievable cases, wherein people took others' lives for the most banal and bizarre reasons.

Each hour-long episode will uncover dark and twisted motives — from vengeance to jealousy — that led to gruesome killings.