20 Cops Who Turned Out To Be Killers

Welcome to WatchMojo, and today we’re looking at terrifying cases of police officers, both past and present, who were uncovered as stone-cold killers.

John Formisano

Newark police officer John Formisano spent over two decades in law enforcement, eventually rising to the rank of lieutenant. From the outside, his professional life appeared stable, but behind the scenes, his personal life was falling apart. In July 2019, amid an ongoing divorce, he forced his way into his estranged wife’s home in Jefferson Township, New Jersey. Once inside, he opened fire, seriously wounding her boyfriend before chasing his wife to a neighbor’s doorstep, where he fatally shot her. Formisano initially claimed he had blacked out, but investigators reconstructed a deliberate sequence of events that pointed to intent. A jury found him guilty of murder and he was sentenced to over seven decades in prison.

Wayne Couzens

Serving as a Metropolitan Police officer in London, Wayne Couzens was part of a unit tasked with protecting government buildings. But even in that trusted position, there were already warning signs in his past. Prior allegations of indecent exposure were reportedly linked to him, yet they weren’t acted upon across multiple opportunities by the force. Then, in March 2021, he used his police credentials to stop 33-year-old Sarah Everard, falsely arresting her under the guise of COVID regulations. He handcuffed her, placed her in a rental vehicle, and drove her to a remote area in Kent, where he assaulted and murdered her. The case sent shockwaves across the United Kingdom—exposing critical failures in police vetting. Couzens later pleaded guilty and received a whole-life sentence.

Nicholas Tartaglione

After graduating from the Westchester County Police Academy in 1993, Nicholas Tartaglione spent years serving across multiple New York police departments. He built a career in law enforcement before everything took a dark turn. Following his retirement in 2008, Tartaglione moved into illegal drug operations, dealing steroids and later cocaine. In 2016, a financial dispute within his criminal network escalated into calculated violence. Tartaglione lured Martin Luna to a bar, kidnapped and murdered him before executing three other men who had witnessed the crime. He buried their bodies in a mass grave which was later uncovered by investigators. In 2024, Tartaglione was sentenced to multiple life terms. It was later revealed he had shared a jail cell with the infamous Jeffrey Epstein.

Jason Van Dyke

On October 20, 2014, Chicago Police Officer Jason Van Dyke responded to a 911 call about a teenager breaking into trucks. Police initially described the suspect Laquan McDonald as erratic, armed with a knife, and refusing commands—an account that justified the use of force. But that narrative would not hold for long. When a court ordered the release of dashcam footage, it showed McDonald walking away when Jason opened fire, unleashing 16 shots as the teen collapsed. The video triggered immediate outrage, leading to murder charges and a later conviction for second-degree murder. He served just over three years before he was released in 2022. Jason’s early release sparked fresh protests and ultimately pushed court-supervised reforms within Chicago PD.

John Christie

English serial killer John Christie returned from World War I and drifted into a life of crime, building a record of theft, fraud, and violent assault in the years that followed. Yet despite that history, in 1939 he was accepted as a War Reserve Constable—a position that gave him both authority and access. In the early 1940s, Christie started luring women to his London flat, where he gassed and strangled them before concealing their bodies. His crimes went unnoticed for years, even contributing to the wrongful execution of Timothy Evans. When bodies, including his wife Ethel’s, were finally discovered in Christie’s home, everything unraveled. After an intense manhunt, Christie was arrested, confessed to multiple murders, and was convicted and executed.

Anthony Sully

Former California police officer Anthony Sully served for eight years before resigning. But after leaving law enforcement, his life took a destructive turn. He turned to drugs, escorts, and escalating violence, eventually turning his Burlingame warehouse into a center of unspeakable horror. Women were lured inside, restrained, assaulted, beaten, and in several cases murdered over a six-month spree in 1983. Some victims were hidden in barrels, sealed with concrete, and dumped across the Bay Area, while others were left along remote roads in San Mateo County. Detectives eventually linked Sully to the crimes through fingerprint evidence, leading to his arrest. He was convicted in 1986 and sentenced to death. After thirty-seven years on death row, Sully died of natural causes in 2023.

Norbert Poehlke

German police officer Norbert Poehlke was employed from 1982 as a high-ranking sergeant in Mühlhausen am Neckar’s canine division. He was seen as a trusted figure in uniform who lived a disciplined family life. But behind that image, financial pressure, debt, and personal tragedy pushed his life into a darker direction. Between 1984 and 1985, Poehlke carried out a series of bank robberies linked to multiple murders across Germany. The rampage earned him the nickname “The Hammer Killer.” His pattern was methodical—he would shoot victims at remote rest stops, steal their vehicles, then use them in armed bank raids. As investigators closed in and suspicion mounted, Poehlke believed exposure was imminent. In October 1985, he murdered his family and took his own life.

Christopher Dorner

Ex LAPD officer Christopher Dorner was dismissed in 2008 after accusing a colleague of excessive force—claims investigators ruled false. He fought the decision through the courts, but every appeal failed. That’s when things took a darker turn. In 2013, Dorner launched a deadly rampage across Southern California, targeting those he blamed for his firing. He killed four people, including the daughter of a former LAPD captain and a responding police officer, while posting a manifesto outlining his motives. The manhunt that followed became one of the largest in the region’s history. Cornered in a cabin in the San Bernardino Mountains after a shootout, Dorner’s violent path came to an end with a self-inflicted gunshot wound to the head.

Mikhail Popkov

Using his police uniform as bait, Mikhail Popkov committed the unspeakable. As a serving officer in Russia, he would patrol at night, offering lone women rides in his police vehicle. Instead of taking them home, he drove to isolated areas where he brutally killed them. His methods were savage and varied, and afterward, he would return home to his family as if nothing had happened. For years, investigators suspected the killer had ties to law enforcement, but the trail went cold. Finally, DNA testing exposed him in 2012. Popkov was convicted of multiple murders—yet the full scale of his crimes kept growing. With dozens of confessions added over time, he’s widely regarded as the most prolific serial killer in Russian history.

Derek Chauvin

On May 25, 2020, Minneapolis police officer Derek Chauvin responded to a call over a suspected counterfeit bill and arrested George Floyd. What transpired was captured on video and sent shockwaves around the world. As Floyd lay handcuffed on the street, Chauvin pressed his knee on his neck for over nine minutes—ignoring repeated pleas that he couldn’t breathe. Floyd was later pronounced dead. It wasn’t Chauvin’s first use-of-force incident, but this time, the outcome was fatal. The footage ignited massive global protests demanding accountability. In 2021, Chauvin was found guilty of murder and sentenced to over two decades in prison, along with a federal sentence. Yet even after his conviction, the case remains deeply sensitive because of the worldwide movement it ignited.

Craig Peyer

California Highway Patrol officer Peyer was arrested in the 1980s for the murder of 20-year-old Cara Knott. On December 27, 1986, Peyer stopped Knott under the guise of a routine traffic check on an isolated overpass. He then attacked her and pushed her off the bridge to her death. The investigation into Knott’s murder revealed a pattern of Peyer's predatory behavior, as other women came forward with complaints about his misconduct. In 1988, he was convicted of Knott's murder and sentenced to 25 years to life in prison. Peyer’s case highlighted the potential dangers of unchecked authority, and underscored the need for increased accountability among law enforcement officers.

Stephanie Lazarus

This Los Angeles detective only faced justice decades after her crime. In 1986, Sherri Rasmussen was brutally murdered in her home, and the crime went unsolved for decades. However, in 2009, DNA evidence linked Lazarus to the crime, revealing a tangled web of jealousy and deceit. Lazarus had dated Rasmussen's husband before their marriage, and her actions stemmed from unresolved romantic jealousy. Her training and position helped her evade suspicion for years. In 2012, Lazarus was convicted of first-degree murder, again highlighting the disturbing truth that even those sworn to uphold the law can commit heinous crimes.

Jeffrey Hall

This Newton, Kansas, police officer was convicted in 2019 for the brutal murder of his ex-girlfriend, Brittany Pfaff. In 2018, Hall, while serving as a patrol officer, shot Pfaff multiple times before setting her house on fire in an attempt to destroy evidence. The case highlighted Hall’s troubling history of domestic abuse and obsession with Pfaff, which escalated to a cruel and murderous end. His actions shocked the small Kansas community he was sworn to serve. In 2019, Hall was sentenced to life in prison without the possibility of parole, marking a grim end to a tragedy that shook the small town and exposed deep flaws in domestic violence prevention.

Antoinette Frank

This former New Orleans officer took part in a brutal triple homicide. In 1995, while on duty, Frank, alongside her accomplice, robbed a restaurant where she had worked off-duty. During the robbery, Frank shot and killed her fellow officer, Ronald Williams, and the restaurant's owners. The crime shocked the community, as Frank had previously been seen as a committed officer. However, her actions revealed a darker side motivated by financial desperation and a sense of betrayal. In 1995, Frank was convicted of the murders and sentenced to death. Her story highlighted the importance of psychological assessments for officers and the potential dangers of unchecked power in law enforcement.

Charles Becker

Becker was a New York City lieutenant involved in one of the most notorious corruption scandals of the early 20th century. In 1912, he was implicated in the murder of Herman Rosenthal, a gambler who had been speaking out against police corruption. Becker, who led the NYPD’s anti-vice squad, was accused of orchestrating Rosenthal’s murder to silence him. The high-profile case exposed widespread issues within the NYPD and jarred the public. Despite maintaining his innocence, Becker was convicted of murder in 1914 and executed in 1915. His case highlighted the dangers of deep-seated corruption in law enforcement.

Gerard Schaefer

A former sheriff's deputy in Martin County, Florida, Schaefer was a notorious serial killer who exploited his position of authority to commit heinous crimes. In the early 1970s, Schaefer was convicted of the brutal murders of two teenage girls, but he is suspected of having killed many more. Schaefer's modus operandi involved using his badge to lure victims, often hitchhikers, before torturing and killing them. His double life as a law enforcement officer and a sadistic killer was revealed when incriminating evidence was discovered at his home, including personal items belonging to several missing women.

Manuel Pardo

In the mid-1980s, this once trusted Florida police officer embarked on a murderous killing spree and took the lives of nine people, most of whom were involved in the business of illegal substances. Pardo, who initially claimed to be ridding society of criminals, justified his actions by portraying himself as a vigilante. However, his methodical killings contradicted any sense of actual justice, revealing a disturbing lust for violence. In 1987, he was apprehended and then eventually convicted of multiple murders, and eventually was executed in 2012, bringing an end to a dark chapter in Florida's history.

Louis Eppolito and Stephen Caracappa

Two New York City detectives became infamous as "The Mafia Cops." During the 1980s and early 1990s, the two men exploited their positions in the NYPD to work as hitmen and informants for the Lucchese crime family. They were involved in at least eight murders, as well as various other crimes, including drug trafficking and kidnapping. Their shocking betrayal of public trust came to light in 2005, leading to their conviction in 2006. Both were sentenced to life imprisonment for their roles in these crimes. The sordid tale of Eppolito and Caracappa highlighted the dangerous potential when officers betray society and align with organized crime.

Joe DeAngelo

A former police officer, DeAngelo gained infamy as the "Golden State Killer." Operating in California from 1974 to 1986, his spree included numerous burglaries and murders. Initially, his law enforcement role helped him evade capture, as he exploited his insider knowledge to avoid detection. However, a breakthrough came decades later, when advances in DNA technology led to his arrest in 2018. DeAngelo’s shocking double life stunned the nation, revealing how he maintained an outwardly normal existence while terrorizing communities. In 2020, he pled guilty to multiple counts of murder and other crimes, ultimately being sentenced to life imprisonment.

Drew Peterson

This former Bolingbrook, Illinois, sergeant became notorious nation-wide after the suspicious disappearances and deaths of two of his wives. In 2004, Peterson's third wife, Kathleen Savio, was found dead in her bathtub, initially ruled as an accidental drowning. However, suspicions grew when his fourth wife, Stacy Ann Cales, went missing in 2007. In light of Stacy's disappearance, Savio's death was reexamined and ruled a homicide. In 2009, Peterson was arrested and subsequently convicted in 2012 for Savio's murder. His disturbing behavior and pattern of domestic violence revealed a chilling abuse of power, as he used his training to evade suspicion. This case, like numerous others, highlighted issues of domestic violence and the need for improved protective measures.

Which of these cases shocked you the most? Let us know in the comment section.