Investigators say 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

"The accused appears to have had no motive for killing the people other than the act of killing itself," prosecutors said.

Part of a nursing service's palliative care team, the 40-year-old doctor whose identity has not been revealed due to Germany's privacy policy was first suspected of murdering four elderly patients in June and July.