The man, identified only as Niels H., 39, has claimed killing perhaps 30 patients with such lethal overdoses, which would make him one of Germany's worst post-war serial killers.

The tall and heavyset man, who was jailed for life in February 2015, has been found guilty of two murders and three attempted murders of intensive-care patients.

He has admitted to injecting some 90 patients with the drug so he could then try to revive them and, when successful, shine as a saviour before his medical peers.

He said he felt euphoric when he managed to bring a patient back to life, and devastated when he failed. Each time he would then vow to himself to end his deadly game, he said, only to strike again soon after.

After the shocking revelations of the nurse's murderous obsession, police and prosecutors launched a special forensic commission dubbed “Kardio” (Cardio) to look into other patient deaths.

They said Wednesday they had now exhumed and tested 77 sets of mortal remains of former patients who had been in the care of Niels H. at the Delmenhorst hospital near the northern city of Bremen.

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Aside from the 24 suspicious cases where traces of the unprescribed drug were found, they said, they were still awaiting test results from seven other bodies.

The sweeping investigation is looking into some 200 fatalities at the hospital and at the nurse's previous places of employment and is expected to take many more months.

The nurse had previously worked at another clinic, an elderly home and an emergency medical service.

The grisly case dates back to 2005, when a colleague witnessed Niels H. injecting a patient in Delmenhorst.

The patient survived and Niels H. was arrested and, in 2008, sentenced to seven and a half years in jail for attempted murder.

Amid the media publicity, a woman then contacted police, voicing suspicion that her deceased mother had also fallen victim to the killer nurse.

The authorities exhumed several patients' bodies and detected traces of the drug in five of them, declaring it either the definitive or possible contributing cause.

These results sparked the trial that sent the nurse to jail for life, but authorities fear the two confirmed murders may just be the tip of the iceberg.

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