Petr Zelenka was born on 27 February 1976 in the Czech Republic. Little is publicly known about his early childhood or education, though reports suggest he trained in basic nursing and medical assistance. He began his professional life as a hospital nurse, eventually finding employment at the Havlíčkův Brod Hospital, located approximately 100 kilometers southeast of Prague.

Zelenka’s colleagues initially described him as quiet and reserved, with no overt signs of instability. However, subtle indications of a controlling and detached personality were noted by some co-workers. His duties placed him in direct contact with patients in fragile medical conditions, including elderly individuals and those in intensive care. This unrestricted access to medical substances later became the instrument of his crimes.

By 2006, Zelenka was fully trusted by his supervisors, and his experience in handling injections, medication, and post-operative care gave him intimate knowledge of both the vulnerabilities of patients and the detection limits of certain drugs. 

Between May and December 2006, Petr Zelenka carried out a series of poisonings at Havlíčkův Brod Hospital, deliberately injecting patients with heparin, an anticoagulant drug used to prevent blood clotting. Administered in correct doses, heparin is lifesaving, but when given in excess, it leads to catastrophic internal bleeding and organ failure.

Zelenka’s attacks occurred across several wards, primarily targeting elderly and critically ill patients. Over seven months, seven patients died and ten more suffered near-fatal bleeding episodes before suspicions arose. His pattern was erratic — patients of different ages, both male and female, were poisoned without clear motive or personal connection.

According to later court testimony, Zelenka carried a hidden vial of heparin and secretly injected his victims, often during night shifts when supervision was minimal. His actions initially confused doctors, as the sudden onset of hemorrhaging in patients without medical cause appeared inexplicable.

It was only after internal audits at the hospital began identifying abnormal coagulation levels in multiple patients that administrators suspected foul play. In December 2006, Zelenka was detained following internal investigation and forensic review. When confronted with the evidence, he admitted to having administered the drug but claimed he had not intended to kill anyone — instead, he allegedly wanted to “test” doctors whom he believed were incompetent and would fail to recognize his actions.

The rationale presented by his lawyer suggested an impulsive compulsion driven by delusion and arrogance, but prosecutors characterized the murders as cold, systematic, and sadistic. The victims, mostly elderly or already in weakened condition, stood no chance once the excessive doses were delivered.