A doctor has been arrested in Berlin on suspicion of killing four elderly patients and trying to cover up the evidence by setting fires at their homes, authorities said Wednesday.

The 39-year-old doctor, who was part of a nursing service’s palliative care team, was ordered to remain in custody on Tuesday pending a possible indictment, police and prosecutors said in a statement. His name wasn’t released in line with Germany privacy rules.

He is accused of killing four patients who were in the nursing service’s care in June and July, though investigators don’t yet know how, and then attempting — with mixed success — to set fires in their apartments.

In the first case on June 11, firefighters who arrived at the scene were able to revive the victim, an 87-year-old woman, but she died at a hospital shortly afterward. On July 8, investigators say, the suspect killed a 76-year-old woman.

The deaths of two more women, who were 72 and 94, followed on July 15 and 24.

Investigators didn’t specify what led to the man’s arrest or say anything about a possible motive. He is being held on suspicion of manslaughter as well as one count of arson and three of attempted arson.