Although the Law & Order franchise features countless people who committed heinous crimes without remorse, many of them have a typical motive such as greed and envy, or sometimes even a good Freudian Excuse, or even a motive one can sympathize with. Some serial killers and others, however, have the (dis)honor to be called a monster.
- Frank Masucci was the franchise's first recurring villain, and one of the worst. Loaning out his henchman Antonio "Tony" Scalisi to a group of corrupt city officials, Masucci had Scalisi kill Councilman Chuck Halsey on their behalf, then had Scalisi murdered after he was released by EADA Benjamin Stone, leaving the officials to take the fall for a racket he was complicit in. Reappearing in "The Torrents of Greed" two-parter, Masucci and his brother-in-law Harv Biegel sent thugs to assault store owners who refused to buy bootleg cigarettes, leaving one man dead and one man crippled. Indicted for, among other crimes, the murder of Trucking Union President Russel Mackey, Masucci sabotaged the prosecution by forcing leg-breaker Joe Pilefski to perjure himself, and had Biegel killed when he became concerned his brother-in-law was getting ready to turn on him. After Biegel and Mackey's bodies—along with over a dozen others—were retrieved from a mass grave site in New Jersey, Masucci found himself re-indicted, only to be assassinated on orders from his sister, Katherine Biegel, who feared, with cause, that she was next on his hit list.
- Constantin Volsky, from season 9's two-part finale "Refuge", ordered an innocent man murdered and dismembered because he had a relative who wouldn't go along with a money-laundering scheme. When he finds out that the key eyewitness for the prosecution is a 6-year-old boy, he sends assassins to kill him. They kill his mother and an A.D.A. The boy lives, but only because they didn't cut deep enough into his throat. In the second part, he orders the bombing of the precinct where the police protagonists work, just for giggles.
- Mark Bruner, from season 14's premier "Bodies", raped and murdered no fewer than 17 teenage girls and kept most of their bodies rotting in an undisclosed location so he could go and admire them as they decayed. He terrified his original defense attorney so much that McCoy helped to get her reassigned, terrified Serena, visibly unnerved Briscoe, Green, and McCoy. What made him truly monstrous was his refusal to reveal the location of his dumping ground so that his victims might be identified, specifically to torture the parents so that they couldn't find closure, and to torture Jack with the knowledge that he couldn't give them that closure.
- Leon Vorgitch, from season 17's "Deadlock", was in prison for killing five people. He then kills two guards and escape from prison. When the detectives come for him, there are even more deaths, including several students from a classroom Vorgitch had taken hostage. When Detective Green asks Vorgitch why he killed the kids, he laughs and says "Why not?" In the end, he brags to Jack and Connie that he will escape again and kill both of them.
- Darryl Kern, also known as The Bowery Stalker, from season 2's "Manhunt", made a habit out of abducting, raping, torturing and killing women; his victims numbered at least 30. He was a former soldier who was discharged because he believed that soldiers enjoyed killing. His journal states that he is planning to survive an upcoming radical war, and create a new generation from sex slaves, but later admits during questioning that he's simply having fun at the expense of the police. When his hideout is found, at least fifteen bodies, later 18, are found buried in his bunker alone, including 3 kids. He also has his assistant, a mentally fragile man named Posey, help him kidnap a woman and her young daughter. Kern then kills Posey, and plans to kill his hostages before he is arrested by Canadian police.
- Arthur Blessard, from season 3's "Redemption", claimed the lives of 21 different women before he was caught. His MO would involve using his job in the IRS to enter the women's homes, and once given access would proceed to bind them to their beds where he would then beat, rape, and even bite chunks of flesh off their bodies before strangling them to death. He first started this in 1983, claiming seven victims in New York City before framing a mentally disabled man, Roger Berry, when the cops were closing on to him. With Roger taking the fall, Blessard went to other cities across the country killing even more women, as well as evolving from strangling to slitting throats. After hearing of Roger's release from prison, Blessard returns back to New York and kills more women there, all so he frame Roger once more and watch him return to prison.
- Matthew Linwood Brodus, from season 3's "Execution", was a criminal on death row. Prior to being captured, he was a killer and rapist who kidnapped women from different places and took them to his hideout. From there he would not only rape, but also torture them for several hours. The victims would succumb to this and die, at which point he would continue to rape their corpses. He has done this to at least 12 women, with the bodies mutilated and disfigured beyond identification. Before his execution could be performed, another victim appeared where he blinded her as well as performing his usual MO. When Detective Elliot Stabler sought to get a confession out him so that the victim's family could get closure, Brodus not only confessed to the deed, while showing absolutely no remorse about it, but as a way to spite him and the family he attacks the detective where prison guards to come then came and brutally beat him down severely injuring him, thus temporarily avoiding his execution.
- Charlie Baker, from season 4's "Dominance", had in the past raped his brother Billy, and then beat up his alcoholic father when they were caught; Charlie continues to beat his father. In the span of a week, Charlie has either killed, or manipulated the weak-willed Billy into killing, around 10 people, but not before forcing them to have sex with each other first. Then he kidnapped two women, killed their boyfriends, and kept them captive on a roof.
- Eugene Hoff, alias Abraham Ophion, from season 6's "Charisma", is the pedophilic leader of a cult of his 100 followers, which included his preteen victims and their families. Hoff separates the married couples, because he said that they couldn't be soldiers of God if they were slaves to the flesh, and uses all the women and girls of his cult for sexual favors, fathering 1 living and 6 dead children with them. His earliest victim was a 4-year-old Jamie Buchman, who her father caught in the same room with a near-naked Hoff, causing his family to leave the church. Growing paranoid, Hoff began to prepare his followers for war, filling their heads with the idea of the U.S. Government coming to kill them. He was also a greedy man, killing John Cramer and lying to his wife for John's million-dollar bank account and only keeping his latest victim Melanie alive so he can claim her two-million-dollar trust fund after their baby is born. Hoff is ultimately a depraved individual who believes himself to be greater than God.
- Victor Paul Gitano, from season 7's "Fault", was a pedophile who lured kids in, regardless of gender, then raped, tortured, and killed them, He had previously molested a 9-year-old-girl, and had also raped and brutally tortured a 12-year-old boy. When trying to hunt Gitano down, things don't quite go as planned. Not only does he kill one of the two kids he had with him in a subway station full of people by slashing the 9-year-old's throat, but he almost killed Benson the same way. Then, when they corner Gitano in a warehouse, he manages to get behind Stabler and hold him at gunpoint with a shotgun. Gitano, despite knowing he'd get caught or killed at this point, outright boasts that he killed the other child he had, who was only 7, and bragged that she was a "slut" and a "real little whore" before killing her, even though he never got the chance to molest her. Even as a teenager, Gitano was bad, having claimed to have sexually assaulted over a dozen children. He is described as not a "classic" pedophile, but as a "sadist...[who]...chooses children because they're just easier to control."
- Luke Dixon, from season 8's "Confrontation", is among the more heinous rapists in the series. As he thinks that children with imperfections shouldn't be accepted by the public, he tries to create a "Master Race" by impregnating his victims. He operates by using master keys to break in his victims house, forcing them to urinate so he could know their menstrual cycles, and raping them again at the day of ovulation. Dixon has done so to 19 women, including one that he murdered after she confronted him, and another who has been raped thrice and committed suicide due to the emotional trauma. Finally, before getting arrested, Dixon attempted to kill Detective Dani Beck with a knife. With the unique nature of his crimes taking Rape Is a Special Kind of Evil to a new level, Luke Dixon, despite not having an inordinately large number of victims, managed to stand out in a series dealing with sexual crimes.
- Adam Grafton, from season 12's "Pursuit", is a sadistic killer and rapist with over forty victims to his name over at least 25 years. Starting as a teenager, Adam would claim his victimssome of whom, including TV host Alicia Harding's younger sister Vanessa, were in their mid-teens at most—in clumps and paralyze them from the chest down by stabbing them in a certain area, rape them repeatedly, and viciously stab them to death to finish them off, but not before stabbing them in their lung, collapsing it and preventing the victim from screaming for help. In the present day, Adam's obsessed with mentally toying with Alicia about his role in her sister's death by stalking her and sending her bloody pieces of old evidence from the case. When Alicia insults him on live TV, Adam flies into a rage and brutally murders EADA Sonya Paxton, including before trying to hunt down and murder Alicia, which leads to his arrest. At the end of the episode, even on death row, he coldly and smugly, if not gleefully, tells Detective Benson about all the women he's killed without so much as a hint of remorse.
- William Lewis, known as "the Beast", is the Arch-Enemy of Detective Olivia Benson. His soft-spoken manner and good looks hide the fact that he is a killer, rapist, and sadistic torturer. Appearing in season 14's finale "Her Negotiation" and in season 15, his MO is going from state to state, under different aliases, kidnapping, raping and torturing women, regardless of age, for hours and even days on end. When he was young, he watched his babysitter get raped and killed in front of him; he describes it as the best day of his life. Eventually he kidnaps Benson, forces her to watch as he kills the father and rapes the mother of his defense attorney. After killing a cop and taking Benson to a house to rape her, he takes a maid and young girl hostage. When Benson turns the tables on him, he deliberately tries to provoke her to kill him, an experience he makes Olivia relive during his trial. After his escape, he kills another cop, rapes a nurse and kidnaps a young girl. When Benson confronts him, he takes her hostage again, but becomes turned off by his initial molestations, so he decides to force her into a game of Russian Roulette. He ends up fatally shooting himself as one last way of tormenting Olivia, figuring she'll be accused of his murder.
- Johnny Drake, alias Johnny D., from season 16's "Undercover Mother" and the season finale "Surrendering Noah", is a brutal sex trafficker and rapist, having spent the past two decades kidnapping women and selling them into prostitution. Often, Johnny would rape them himself or order his men to gang rape them. One of his victims was a young woman named Eli, with whom he conceived a child. When first arrested, Johnny is caught with four prisoners in his hideout, taking one of them at gunpoint. Johnny is charged with seventeen accounts of kidnapping, rape and trafficking, but learns of his son Noah, whom Benson is adopting; he decides to use Noah as his ticket to freedom, making Benson out to be a woman with a vendetta, and seeks parental rights for Noah to spite Benson's wish not have Noah be part of that kind of life. To intimidate his witnesses, he has one of his pimps murdered, but when five of them testify anyways, he snaps in court, taking one officer hostage, and shooting another officer and the judge, before killing said hostage and attempting to kill Detective Nick Amaro.
- Tommy Onerato, from season 4's "Death Roe", is a cruel master manipulator who runs a successful restaurant with his daughter and son-in-law, who had recently gone missing. When a restaurant food critic is killed simply because she gave a previous--and later to be discovered poisoned--meal at the eatery a bad review, he allows his daughter's husband to take the blame because it appears that he did it in order to save the restaurant. While it is initially suspected that the son-in-law either is on the run or had committed suicide, it's later discovered that Onerato killed the man himself and put his remains through a meat grinder, due to him both trying to break away and start his own restaurant and a family with his daughter, whom we later learn he had been sexually abusing since she was a little girl to the point that he looks at her only as a sex object instead of his own flesh and blood. He then tells her that it was a good thing not to become pregnant, viciously telling her that Children Are a Waste. Even as he is arrested for both murders, it's still seen as a hollow victory, as he has still managed to ruin the business and the daughter's livelihood, leave her a psychologically damaged young widow and boast to her as he was being led away that no one else will ever want her once the truth comes out about the true nature of their relationship.
- Frank McNare, from season 4's "Shibboleth", nicknamed Body By Jake or BBJ, killed physically fit young women by stripping them down to their underwear and hog-tying them up by their necks and right ankle, and, when they would get tired of holding their position, they would strangle themselves. He had eluded the authorities since the 1980s and would send taunting letters to them over the years saying they were too stupid to capture him. While killing his most recent victim, he had called the cops before her death with the anticipation that she would, only for the dispatcher to hear the woman's last words being her begging for her life. McNare had abruptly stopped the killings because he had married a woman who let him torture her, but once she was diagnosed with cancer and as was dying of the disease, he resumed the homicides. Upon finding out the son he had willingly abandoned years earlier-yet had refused to let his stepfather properly adopt him—was a viable suspect in the most recent killing, he was more than pleased to let him take the fall for all of them, even though the man only had knowledge of anything about it because as a child he found a picture of one of his that left his scarred. Even as the son was still willing to go to trial for six murders, Goren allowed him to overhear McNare bragging to Eames about how pathetic and weak he is and how glad he was able to get him out of his hair, not feeling the least bit remorseful for any of his actions. In being convinced by Goren that he was nothing like him, his horrified and visibly upset son gave him up and as he called him out on his behavior upon his arrest, McNare disowns him one final time.
- Chesley Watkins, from season 5's "To The Bone", is a foster mother driven by greed and complete control/obedience of others. She has taken in several young boys, raised them as her own and years after they aged out and she is no longer able to collect the money for having them, brought back a few of her more loyal sons and taught them to commit robbery and murder for money. She had the men rob various homes of their valuables and kill any and all occupants inside by using a machete. She then sets up an investigating officer to be killed by Logan in a twisted effort to try and stop one of her sons involved in the crime, Antonio, from being killed and convince the man to turn himself in, before having his brothers brutally stab him anyway before he's able to speak with detectives. As she and her other sons are then arrested, she throws Logan's own troubled relationship with his mother back in his face while being interrogated by him and lawyering up, refusing to answer any more questions. In a final act of power, she tricks one of her other sons, Floyd, into confessing to the crimes and in proving his loyalty one last time, he commits suicide via jumping out of a window, allowing her not to be charged in the murders and the strong belief that she will only continue to manipulate more children into killing.
- Law & Order Episode & Homicide: Life on the Street Episode : Colonel Alexander Rausch is a former intelligence officer turned racist killer. He manipulates the recently-laid-off Brian Egan into setting off a gas bomb of silver arsenic on the New York Subway, killing 20 black people and injuring others. Several years earlier, he had Egan commit a similar attack on a Baltimore church, resulting in six fatalities, all black people. Once Egan is captured, Rausch kills Egan's wife to prevent him from talking, with Egan's teenage son surviving due to hiding. When captured, Rausch admits that his goal is to provoke a race war, claiming he wants "the mongrels to stop feeding on the hard work and good faith of the rest of us", and that when "you have a cancer, you cut it out".