Edson Isidoro Guimarães was born in 1957 in Rio de Janeiro, Brazil. Details about his early life are scarce. He worked as a nursing assistant at the Salgado Filho Hospital in the Méier district of Rio de Janeiro. His role involved caring for patients in the emergency department, where he had access to various medical supplies and equipment.

Between January and May 1999, Guimarães is suspected of causing the deaths of up to 131 patients under his care. He administered lethal doses of potassium chloride or removed oxygen masks from patients, leading to their deaths. He claimed to have selected patients who were terminally ill or in irreversible comas, aiming to alleviate their suffering. However, investigations revealed that he received payments from local funeral homes—approximately $60 per death—for notifying them promptly about patient deaths, suggesting a financial motive.

Guimarães was apprehended on May 4, 1999, after a hospital porter witnessed him filling a syringe with potassium chloride and injecting it into a comatose patient, who died immediately. Following his arrest, he confessed to five murders. On February 21, 2000, he was convicted of four murders and sentenced to 76 years in prison.

Guimarães' case brought attention to the so-called "Funeral Mafia" in Brazil, where hospital workers received commissions from funeral homes for referring deceased patients. This unethical practice highlighted systemic issues within the healthcare and funeral industries in the country.