Richard Angelo was born on August 29, 1962, in Long Island, New York. His mother was an economics teacher, and his father worked as a high school guidance counselor in the Lindenhurst school district. Angelo graduated from St. John the Baptist Diocesan High School in 1980. After high school, he attended Farmingdale State College, where he completed a two-year nursing program and was known as an honor student.

In October 1987, Richard Angelo came to public attention when he was suspected of poisoning a patient at Good Samaritan Medical Center. He was accused of injecting Gerolamo Kuchich with pancuronium, a muscle relaxant, which made the patient feel unwell. Kuchich called a nurse for help, and Angelo was later arrested for assault, as he matched the description given to the police.

After his arrest, Angelo confessed to poisoning other patients with pancuronium and Suxamethonium chloride, both paralyzing agents used in anesthesia. Investigations led to the exhumation and examination of as many as 30 recently deceased patients to check for traces of these drugs. Angelo was suspected of poisoning at least 35 people during his seven months at the hospital, although the medical examiner could not conclusively link the deaths to the injections. Angelo claimed his motive was to be seen as a hero by saving the patients he had poisoned.

He was held in Suffolk County Jail for more than a year, awaiting trial, and chose not to pay his $50,000 bail due to safety concerns. During his trial, 32 witnesses testified, and more than 100 exhibits were presented. Angelo was ultimately found guilty of multiple charges, including second-degree murder and assault, and was sentenced to 61⅓ years to life in prison. He is serving his sentence at the Great Meadow Correctional Facility and will be eligible for parole in 2049.