When former nurse Niels Högel was convicted of murdering 85 patients at two German hospitals, he became what is thought to be the country’s most prolific peacetime serial killer.
Högel, who was jailed for life on 6 June, is the latest in a long list of healthcare professionals put in prison for taking the lives of those in their care.
One simple question arises above all else in the case of Högel and others like him: Why did they kill?
Offenders rarely talk, and even when they do, “we should be cautious about believing them,” said Elizabeth Yardley, Professor of Criminology at Birmingham City University.
An offender may claim to have taken a patient’s life to end their suffering.
This is how American nurse Charles Cullen, who admitted killing at least 29 patients, explained his behaviour, although this was discredited as some of his victims were in recovery.
“Their words are not truths but performances,” Ms Yardley said.
Others may kill in order to get rid of what they see as difficult patients.
In a confession, Canadian killer nurse Elizabeth Wettlaufer described feeling deep anger at her eight victims, whom she injected with fatal doses of insulin.