A German nurse serving a life sentence for two murders has been charged with killing 97 additional patients, prosecutors said Monday.

The new indictment against Niels Hoegel was expected after officials said in November he may have killed more than 100 patients in total.

Hoegel, who worked at a clinic in Oldenburg from 1999 to 2002 and in Delmenhorst from 2003 to 2005, was convicted of two murders and two attempted murders in 2015.

During his trial, Hoegel said he intentionally brought about cardiac crises in about 90 patients in Delmenhorst because he enjoyed the feeling of being able to resuscitate them.

Those statements prompted investigators to carry out toxicological examinations on dozens of other patients who died at the hospitals, which led to new charges.

GERMAN CITY BANS NEW REFUGEES AMID ANTI-MIGRANT MOOD

It wasn't immediately clear when a new trial at the state court in Oldenburg might start. Additional convictions could affect Hoegel's possibility of parole, but there are no consecutive sentences in Germany.

Of the new cases, 62 involve patients who died in Delmenhorst and 35 patients in Oldenburg. Prosecutor Martin Koziolek said that, in three further cases investigators viewed as suspicious, tests didn't produce enough evidence to add them to the charge sheet.

Hoegel used a variety of drugs in his resuscitation attempts, Koziolek said. He added that prosecutors believe Hoegel "in all cases at least accepted the death of the patients as a result of the effect of the drugs."

As part of a wider investigation involving both hospitals, police and prosecutors reviewed more than 500 patient files and hundreds more hospital records. They also exhumed 134 bodies from 67 cemeteries, and questioned Hoegel six times.

Hoegel could have been stopped earlier if local health officials hadn't hesitated in alerting authorities, police said.

Criminal cases against former staff at the medical facilities are also being pursued.

The Associated Press contributed to this report.