BERLIN (AP) — A doctor who was arrested in Berlin in August is now suspected of killing eight patients and in some cases trying to cover up the evidence by setting fires, investigators said Thursday.

The unidentified doctor, who was part of a nursing service's palliative care team, was suspected at the time of his arrest of killing four elderly patients in June and July and then attempting with mixed success to set fires at their apartments.

Police and prosecutors said Thursday that additional cases surfaced when they examined patients' files and carried out forensic examinations of suspected victims, two of whom were exhumed.

In the earliest case, he is a suspected of administering a lethal mixture of medicines to a 70-year-old man in January. In a similar case in early April, the alleged victim was a 61-year-old woman. A few weeks later, he is alleged to have killed an 83-year-old man in his room at a Berlin hospice with a mixture of medicines.

In the fourth new case, in June, he is alleged to have killed a 70-year-old woman at her apartment and then set a fire. Firefighters were able to prevent the blaze spreading to the rest of the building.

The 40-year-old doctor was originally arrested on suspicion of manslaughter, arson and attempted arson. Prosecutors said they are now treating the cases as murder because the suspect appears to have had no motive other than killing the patients.

The suspect's name hasn't been released, in keeping with German privacy rules. Prosecutors say he hasn't yet responded to the allegations.