A crime-solver in a Police Procedural who has killed and is The Atoner because of this. Their method of atoning is to catch other criminals. Because they can think like criminals, they are often better at this than the average cop.
Interestingly, this motive even applies to people whose killing was perfectly legal—people who served in the military, the FBI, or a spy agency. It also applies to detectives whose killing, and thus whose need to atone for it, is ongoing.
A Vampire Detective Series is a supernatural version of this.
Compare Recruiting the Criminal.
Beware if one of these has a FaceHeel Turn.
- Charlie Parker, the eponymous detective from a series of books by John Connolly, embodies this trope. He slips off the deep end after the death of his wife and child and spends the rest of his life making up for what he did after their death. He's still not shy about killing people though - he just makes sure that the people he's killing are truly evil. The Black Angel suggests that this is the whole reason for Parker's existence in-universe. He is one of the angels the fell from heaven after Lucifer's revolt, but rather than descending to hell, he became stranded on earth, spending his many lifetimes helping others - dead and alive - in penance for his sins. However, the ending of The Wrath of Angels seems to refute this theory - according to various in-universe authorities there is a fallen angel present in the series recurring cast, but it isn't Charlie.
- ColonyMars has Mia Sorelli, a sort-of inversion in that she was recruited for her police experience, having emigrated to Mars to build a new life after a period of alcohol and drug use.
- At the beginning of Death of a Nationalist Carlos Tejada shoots an unresisting suspect out of hand, because he believes she's guilty of murder. When he finds out that she was innocent, he devotes the rest of the book to trying to find the real killer. Throughout the rest of the series he tries to make amends to her family, with mixed results.
- Dirk Gently becomes this in his second novel. Technically he was a detective beforehand, but only on paper; it's just a scam to swindle wealthy little old ladies with missing cats while he claims that periodic trips to the Bahamas and large bar tabs are necessary expenses for his work. One client makes the ludicrous claim that a giant monster with a scythe is stalking him, and hires Dirk to protect him, which Dirk puts his usual amount of effort into doing, i.e. none. When said client actually winds up murdered, Dirk feels uncharacteristic guilt and resolves to actually solve the case even though said client is no longer able to pay him.
- In Discworld, Commander Vimes has killed a lot of people, and even though they were mostly self-defence, he's aware that he wasn't really thinking about that when he killed them. He explicitly tells The Dragon in Snuff that he recognised him as a killer the moment he saw him - because he's used to seeing a killer's face every day in his own mirror.
- In the "Father Brown" stories by G. K. Chesterton, Father Brown (the series detective) meets and bests a thief named Flambeau, who, because he wants to atone for his crimes (Brown having stopped him from going down the slippery slope when he was going to frame someone for his crime), then assists Father Brown in solving crimes by providing information about how professional criminals work.
- In Larry Niven's Gil the Arm stories, Gil Hamilton lost an arm in an accident in space. However, only prosthetics are available in space, as accidents in space tend to quickly ruin transplant stock and the minarchist Belters don't regularly execute "criminals" for their organs. He thus immigrates to Earth to take advantage of the UN-sponsored organ harvesting programme, justifying it to himself that his new arm would most likely come from an executed murderer (perhaps unaware that the UN government regularly has people broken up for running traffic lightsnote ). Surprise - his brand-new limb came not from a villain, but from the seized stockpile of a criminal who killed people for their organs. Lacking the moral composure to have the arm removed, he joined the Amalgamated Regional Militia (aka ARM), the agency which polices illegal body harvesting... but spends more time suppressing inconvenient technologies and hunting illegal pregnancies.
- Skulduggery Pleasant: It's never given as an explicit reason why he became a detective, but he does have a very dark past which includes having once been exactly the sort of mass-murdering supervillain he now spends his days defeating.
- Jerry Spinoza of J.R. Rain's The Vampire with the Dragon Tattoo became a private detective after his drinking led to the death of his son. He specializes in missing child cases in hopes of repaying his debt by saving the children of others.
- In Body of Proof, former neurosurgeon Megan Hunt is trying to atone for killing a patient on the table after neurological damage causes her hands to numb occasionally. She becomes a medical examiner because she can't kill anyone if they're already dead.
- Seeley Booth in Bones (Ex-sniper) He actually voiced this as his reasoning for joining the FBI.
- A supporting character on Bones was secretly working for a villain while he was doing the lab work to solve other crimes...
- Ezekiel Stone of Brimstone killed the man who raped his wife. When Ezekiel was later killed in the line of duty he was sent to Hell because, no matter how deserving of death the rapist had been, Stone's actions had been motivated by anger and the need for revenge instead of a desire for justice. The Devil sent him back to Earth to hunt down and return 113 escaped souls with the promise of a chance at entering Heaven (Not a guarantee, just the offering of a chance) if he captured all the escapees. Notably, Ezekiel has no personal regrets about what he did.
- Castle: Captain Montgomery spent his career trying to atone for his actions as a rookie, when among other things he was complicit in the death of Beckett's mother.
- Horatio Caine in CSI: Miami (Kinda) He tries to catch as many murderers as subject him to Suicide by Cop. Preferably not by Suicide by Cop.
- Mac Taylor in CSI: NY (Former Marine, served in Beirut and Afghanistan). Says to one young perp who thinks he's tougher than Mac because he shot some people, "I'm a Marine, you little punk. I've put men in the ground on foreign soil so you can sleep at night, but you wouldn't know anything about *that*, would ya - *kid*?"
- The Cowboy Cop protagonist of the show Maou became a detective out of guilt over having accidentally killed someone when he was younger (and having been let off scot-free because his rich and influential father pulled some strings).
- Patrick Jane of The Mentalist didn't kill anyone, he just scammed many people out of lots of money as a wildly successful fake psychic. But after he offended a serial killer by doing a cold read of him on television, his family was murdered. Jane (eventually) became a police consultant in pursuit of a chance at revenge. He's not exactly "atoning" (or giving back the money), but he is deeply ashamed of his past actions as a con artist and seems to hope that he's become a man his dead family would be proud of.
- Leroy Jethro Gibbs in NCIS (Former Marine sniper) Gibbs also killed his wife's and daughter's murderer, although he has stated that he "never lost a day of sleep over [him]".
- He never really killed, but Sebastian Stark of Shark was once a defense attorney . However, after one of his clients who he managed to get acquitted went on to kill his wife shortly after, Stark switched teams and becomes a prosecutor.
- L.A. Noire's Cole Phelps was a Marine in the war. Specifically, he was The Neidermeyer who ended up leading an attack on Japanese civilians.
- A less severe example in Phoenix Wright: Ace Attorney is Ron DeLite, a former thief, opening a security business that helped other businesses defend themselves against thieves. Of course the twist is that he then turns around and sells the plans to other thieves. At least his wife's in on it this time.
- The Suikoden series has the Oboro Detective Agency in Suikoden V.
- A Miracle of Science: The primary protagonist Detective Benjamin Prester is a reformed Mad Scientist who, after being treated for Science-Related Memetic Disorder himself, now works to bring in others for treatment and protect everyone else from their rampages. Most of his work involves applying psychology to get the mad scientists into a position where they lose momentum and surrender. He later loses his job after a relapse, and ends up becoming a liaison between Mars and the unmodified remainder of the human race.
- Career con man Frank Abagnale, Jr. (on whose life the Leonardo DiCaprio film Catch Me If You Can was based) eventually settled down and became a high-profile securities consultant who specialized in the sort of crime he used to commit. It is also notable that to this day he has never taken money from law enforcement for his consultation, even refusing reimbursement for travel expenses.
- Eugène François Vidocq, a criminal-turned-detective who is notable for creating the very first private detective agency in Real Life.