Sean M. Lannon was born on March 3, 1974, in the United States. Little is publicly known about his upbringing or early years, but his later life was marked by troubled relationships and personal turmoil. He eventually married Jennifer Whitman, and the couple had children, but their marriage ended in divorce. Lannon relocated between New Jersey and New Mexico over the years, maintaining a presence in both states. He had no widely reported criminal history before the killings of 2021, but his later statements to police painted a disturbing picture of his mindset and alleged past experiences. During questioning after his arrest, Lannon claimed to have been sexually abused as a child by Michael Dabkowski, a man he would later kill. He also made the shocking claim that he had killed a total of 16 people, though only five murders have been confirmed.

The string of murders attributed to Lannon began in January 2021 in Grants, New Mexico. Investigators believe that during this time, Lannon killed his ex-wife, 39-year-old Jennifer Lannon, along with two men—40-year-old Jesten Mata and 21-year-old Matthew Miller. Prosecutors allege that Lannon dismembered the three victims. He then allegedly enlisted 60-year-old Randall Apostalon to help move the remains using a pickup truck. At some point afterward, Lannon killed Apostalon as well.

The bodies of all four New Mexico victims were discovered on March 5, 2021, in a vehicle parked at the Albuquerque International Sunport parking garage. Their discovery came weeks after family members had reported three of them missing. The killings shocked the community and prompted a multi-state investigation.

Only three days later, on March 8, 2021, in East Greenwich Township, New Jersey, Lannon bludgeoned to death 66-year-old Michael Dabkowski, a man he accused of sexually abusing him during his youth. After the killing, Lannon stole Dabkowski’s vehicle and fled. He was arrested two days later in Missouri after police identified him driving the stolen car.

Following his arrest, Lannon confessed to the confirmed killings and reiterated his claim of having murdered a total of 16 people—15 in New Mexico and one in New Jersey—though authorities have found no evidence to corroborate additional murders.

Lannon was first prosecuted in New Jersey for Dabkowski’s murder. In October 2022, he pleaded guilty to the killing, and in December 2022 he was sentenced to 35 years in prison. Afterward, he was extradited to New Mexico to face charges for the four other murders. In May 2024, Lannon pleaded guilty to all counts and received four consecutive 15-year sentences, totaling 60 years. Under the terms of his plea agreement, he will serve his New Jersey sentence first before being transferred to New Mexico to serve the remainder of his prison term.