While Dr. Michel Joseph Swango eventually pleaded guilty to four murders, his victim count may be as high as 60.

A doctor has an unnatural obsession with death. When the FBI gets involved after a string of mysterious deaths, they discover a 20-year-long trail of destruction that leads them on an international hunt to stop a sadistic madman.

Dennis Cashman, a judge from Quincy, Illinois, remembers overseeing the case of Michael Swango, who had been charged with poisoning his paramedic co-workers at a local hospital. Worried Swango could be a potential danger during the trial, Cashman ordered a padlock to be placed on an ice machine so Swango could not have access to it and potentially harm more co-workers.

Billy Meyer, a chief investigator with the Quincy Police Department, recalls investigating Dr. Michael Joseph Swango, who had been accused by his paramedic co-workers of poisoning them. Swango was arrested in October 1984 for poisoning his co-workers, and during a search of his apartment, police found Tero ant poison, books on Satanism, guns, survival knives and recipe cards for pesticides, botulism and cyanide mixtures.

James McCarthy, a former FBI Special Agent, recalls going to interview Michael Joseph Swango, a former physician and serial killer who poisoned patients and co-workers, in prison. Swango pleaded guilty to murdering four victims in 2000, and he is currently serving four life sentences at the ADX Florence supermax prison near Florence, Colorado.

So many patients died under the care a Clinton, Indiana, nurse that co-workers began to joke that he was the “Angel of Death.”

After Efren Saldivar's co-workers encountered a string of surprising deaths, rumors began to circulate around Glendale Adventist Medical Center about his “magic syringe.”

Detective Tony Futia discusses arresting and interrogating Efren Saldivar, a respiratory therapist and serial killer. Saldivar later pleaded guilty to killing six victims and attempting to kill a seventh, admitting that he murdered patients through methods such as suffocation or lethal injection with drugs like Pavulon and succinylcholine chloride, which halt breathing.

Sergeant John McKillop from the Glendale Police Department recalls the investigation of Efren Saldivar, who pleaded guilty to the murders of six patients and the attempted murder of another patient. Saldivar killed his victims through methods such as suffocation or lethal injection, using drugs like Pavulon and succinylcholine chloride to halt their breathing.

Dr. Terry Dubrow discusses the minds behind murderers in the medical field.

In one of serial killer Dr. Joseph Michael Swango's cases, a pregnant patient accused him of injecting her with an unknown substance, shortly after which she went into convulsions. The patient survived and told nurses at the hospital what happened, but Swango denied any wrongdoing. Following suspicion from medical authorities, his privileges were suspended, and Swango fled the area.

Detective Will Currie from the Glendale Police Department remembers interviewing Efren Saldivar, who pleaded guilty to the murders of six patients and the attempted murder of another. Detective Currie called in Saldivar for his initial interview, and although Currie did not have a lot of information about the respiratory therapist's murders, he wanted to "keep [him] talking."

Quincy Police Department Chief Investigator Billy Meyer recalls searching Dr. Joseph Michael Swango's disturbing "house of horrors." Meyer says he was "totally shocked and amazed at the same time" after finding "one giant chemistry lab" at Swango's apartment, which was mostly filled with deadly poisons and recipe cards for various toxins.