Season 1

May 1988. Detectives investigate the discovery of the body of 86-year-old Alice Covington inside her car outside the city of Raleigh, North Carolina. The remote location and the 'vampire-like' burn marks on Covington's neck immediately raise their suspicions. Investigators hit the streets for clues. They learn the elderly woman was seen struggling with a female nurse before she disappeared. A bank-teller reports she cashed a $2500 cheque on Covington's account when she and a nurse pulled up at drive-thru bank. Detectives question Covington's friends and identify homecare nurse, Carlette Parker, as the prime suspect responsible for her demise. When they research her background, they discover she has a history of stealing from those in her care.

1984. Tampa, Florida. Police discover the bodies of multiple murder victims. All show signs of horrific sexual abuse. A serial killer is on the loose. The only pieces of evidence investigators have connecting the murders are minute red fibres that they believe come from the killer's car. When the same fibres are found on teenage rape victim Lisa McVey, police get a vital breakthrough. Despite being blindfolded and repeatedly raped, the teenager's testimony helps police identify her attacker. He is Bobby Joe Long an X-Ray technician with a history of deviant behaviour while working in Tampa's hospitals. When detectives present Long with evidence linking his car to the murders, he confesses and describes each kill in detail.

Missouri, December 1984. St Louis Police are called in when a farmer discovers the body of a young man, Sean Cavaness. He's been shot twice in the head and left to die at the side of the road. Investigators immediately begin searching for leads to uncover who could have murdered the man and are shocked when they realise that their prime suspect is none other than the victim's father, Dr John Dale Cavaness. 'Dr Dale' as he's known has established himself as a hero in his hometown of Eldorado, Illinois where he regularly offers his medical services for free to those unable to pay. Locals cannot believe that this charming and kindly doctor could be capable of murdering his own son. But when police delve into his past, they reveal a shocking history of violence and a desperate doctor, battling with financial problems.

When young carer, Suzette Trouten goes missing, Kansas police are drawn into the dark world of one of America's most despicable killers. Former X-ray technician and medical consultant, John Edward Robinson appears to be an upstanding member of the community. But investigators soon discover he is not who he seems. Behind the mask of respectability, he hides a history of crime, lies and depravity. Detectives uncover a seemingly innocent connection between Suzette and Robinson. She moved state to take up nursing work contracted through his company. But there's something else. She and Robinson both participate in BDSM - bondage, domination and sadomasochism. They know each other from online forums, catering for those with extreme sexual tastes. Police discover Suzette isn't the only missing person connected to Robinson.

When retired nurse Joyce Brannon is discovered brutally murdered, Chicago investigators face one of their toughest challenges yet. There is no forensic evidence, no fingerprints and no murder weapon. The murder appears without motive and it seems that whoever killed Brannon has committed the perfect crime. But when the FBI learns that the victim has been issued with a subpoena to give evidence against a suspected fraudster, they have their suspect. Dr Ronald Mikos is a highly successful Chicago podiatrist who has been under investigation for eighteen months by Chicago's Department of Health and Human Services. This charming and highly successful doctor is the highest earning podiatrist in the state and investigators suspect that he could be swindling the federal government for hundreds of thousands of dollars. But when they attempt to uncover his crimes, they hit a brick wall. Mikos' patients are loyal to their doctor and no-one is prepared to testify against him.

When lovesick nurse Martha Beck falls for dashing businessman Raymond Fernandez the result is murder. Jilted nurse Martha Beck is desperate to find love. Unmarried, with two kids, and a childhood traumatised by bullying and sexual abuse, she dreams of finding her knight in shining armour. She advertises in a Lonely Hearts column and gets a response from charming romantic Raymond Fernandez. Martha believes she's met her perfect partner and the pair begins a whirlwind romance. But Fernandez is not who he seems. The Hawaiian born sailor is in fact a conman, turned psychotic from an accident at sea. During a spell in jail he learned the darks arts of voodoo and sexual seduction and uses his new-found skills to ensnare lonely women and defraud them of their riches. Opposites attract, large Martha and skinny Raymond form a murderous partnership cemented with taboo sexual practices. Hungry for cash the passionate lovers lure and con desperate women through the Lonely Hearts columns. But there's one small problem with their plan. The more Raymond seduces these women the more jealous Martha becomes. Her delusional love will provoke a calamitous killing spree, which will make Martha Beck and Raymond Fernandez two of the most notorious serial killers in American history. They will commit horrific cold-blooded murder of the most despicable kind. Martha and Raymond's true romance will see them poison, bludgeon and shoot their way into the history books and pay the ultimate price.

March 1987. A Cincinnati coroner autopsies John Powell, a patient who has recently passed away in the city's Drake Memorial Hospital. Powell had been in a coma since a motorcycle accident - his death comes as no surprise. But as the coroner cuts into Powell's stomach he smells burnt almonds. The odour is unmistakable. It's that of the deadly poison Cyanide. The coroner records Powell's death as homicide. Police begin their investigation and receive information regarding an orderly's suspicious behaviour. His name is Donald Harvey. Colleagues call him the Angel of Death due to the number of deaths that occur on his watch. Incredibly, Harvey confesses to killing Powell, claiming he did it out of mercy. Prosecutors charge him with murder but deem it unlikely they'll find evidence that he has killed before. But local news anchor Pat Minarcin is suspicious and takes it upon himself to investigate. Whistle-blowers secure patient records and Harvey's time sheets. Minarcin discovers that Harvey is always on duty when a patients dies. Believing he's uncovered a serial killer, Minarcin calls Harvey's attorney, William Whalen, for comment. Whalen doesn't talk and instead challenges his client to come clean. Harvey admits to killing dozens over an 18-year period and begs his attorney to save him from the executioner. The only option is a plea bargain, admit everything in return for life imprisonment. Prosecutors agree and over the coming months Harvey confesses to over 80 killings making him one of the most prolific serial killers in American history.

November 5th 2009. Fort Hood, Texas: the most populous US military base in the world. Here soldiers assemble for final medical exams before deployment overseas. As they wait in line, a uniformed man stands, draws a handgun and begins shooting. He kills 13 and injures 32. The massacre is halted when a civilian police officer shoots and wounds the gunman. He's identified as Army psychiatrist, Major Nidal Hasan. Investigators charge him with murder and scour his background for his motives. Hasan is the son of Palestinian immigrants. He joins the Army and trains to be a doctor. After the 9/11 attacks he's bullied by his colleagues and becomes insular. He becomes an Army Psychiatric intern, but is considered to be a loner and speaks out against the wars in Iraq and Afghanistan. In 2009, his world is turned upside down when he's told he must deploy to a war zone. Soon after his transfer to Fort Hood, he buys a powerful handgun and forbids anyone from entering his apartment. The day before the shooting, he gives away many of his belongings to his neighbours and urges them to read the Qu'ran. He then travels to Fort Hood? and unleashes mayhem. Hasan's trial reveals he was in contact with a radical Muslim cleric and that he openly praised a terror attack on US soil. The military court weighs up the evidence and sentences Hasan to death. But question remain. Was Nidal Hasan a crazed lone gunman... or was he a jihadist?

When officials at the Community Hospital of the Valley in Perris, California notice a suspicious cluster of patient deaths, a whistleblower contacts the coroner's office. The resulting investigation leads to the exhumation of 38 bodies from local cemeteries. Tissue analysis confirms the level of the muscle relaxant drug Lidocaine in these bodies is 10 to 20 times higher than normal. Whereas an average dose is 100 milligrams, they contain 1000 to 2000 milligrams - enough to kill. Investigators dig deeper and quickly discover one particular nurse was on duty when each of the patients died. His name is Robert Rubane Diaz. Police raid Diaz's home and find empty Lidocaine boxes in the trash. Prosecutors charge him for the murder of 12 patients and delve into his past to uncover his possible motive to kill. They reveal he's a fantasist, resentful of the fact he's not smart enough to be a Doctor. They theorise he engages in a dangerous game of life and death - purposely worsening patients' conditions with overdoses of Lidocaine, before bringing them back from the brink of death in the presence of medical doctors to make himself look good. But then, somewhere along the line, he discovers he gets a kick out of killing and the body count quickly rises. The evidence presented at his trial is damning and the judge sentences Diaz to death by lethal injection. After 26 years on death row, Diaz died in 2010 from natural causes. He never admitted his crimes.

Kimberly LaGayle McCarthy (May 11, 1961 – June 26, 2013) was a death row inmate who was convicted and sentenced to death for the 1997 murder of her neighbor, 71-year-old retired college professor Dorothy Booth, in her Lancaster, Texas (Dallas–Fort Worth area) home during a robbery. She was also a suspect in the murders of two other elderly Texas women, for which she was never tried. McCarthy was born on May 11, 1961, in Greenville, Texas. She worked as an occupational therapist in a nursing home. She was briefly married to Aaron Michaels, with whom she had one son. During her adult life, she developed an addiction to crack cocaine.