A German nurse convicted of killing two patients with lethal doses of heart medication may have murdered at least 84 others, investigators said Monday.

Niels Hoegel was convicted of the two murders, as well as two attempted murders, in 2015. He worked at a clinic in Delmenhorst, an urban district in Lower Saxony, at the time, ITV reported.

As part of their investigation into Hoegel, authorities exhumed hundreds of bodies of the nurse’s former patients, both in Delmenhorst and nearby Oldenburg.

The resulting evidence suggests that he may have killed at least 84 more people, officials said.

Authorities say “at least,” because other patients were cremated, destroying any potential evidence, according to the report.

“Eighty-four killings … leave us speechless,” Oldenburg Police Chief Johann Kuehme told the station. “And as if all that were not enough, we must realize that the real dimension of the killings by Niels H is likely many times worse.”

Kuehme claimed that the deaths could have been prevented if the clinic staff at the time had alerted police and prosecutors right away to Hoegel’s murderous streak — and authorities are pursuing criminal cases against those employees, according to the report.