A former German nurse now serving a life sentence in prison for murdering two patients is suspected of killing scores of others, media reported on Monday.

At least 84 patients of the convicted nurse, identified as Niels Hogel, 40, were found to have died after suffering from injections of five different deadly drugs, according to police.

The conclusions were based in part on toxicology tests on the remains of his 134 former patients, who were exhumed to see if they contained traces of the chemicals the nurse had confessed to using, reports said.

Authorities are waiting for the results of more toxicology reports, which could drive the number of confirmed deaths even higher, police added.

If Hogel were to be found guilty, it would make him one of the country's worst serial murderers, German news agency DPA reported.

In 2015, Hogel was sentenced to life in prison by a court in the northern German city of Oldenburg on two counts of murder, two counts of attempted murder and causing bodily harm to patients.

In past hearings, Hogel confessed to intentionally injecting patients at two clinics in northern Germany with deadly drugs that can cause heart failure or circulatory collapse so he could take "heroic" measures to try to revive them, media reported.