A doctor in Germany has been arrested in Berlin after being suspected of killing four of his elderly patients, police said Wednesday. 

The 39-year-old doctor worked as a palliative care nurse. He was detained on Tuesday on suspicion of manslaughter.

"The accused is suspected of killing four female patients in the care of the nursing service between June 11 and July 24 in an as yet unknown manner and then setting fire to their homes," police said.

The fire brigade was forced to put out some of those fires at the time.

What do we know about the deaths?

Police said the first case occurred on June 11. Firefighters arrived at the scene and were able to resuscitate the 87-year-old woman, but she later died in the hospital.

The doctor then allegedly killed a 76-year-old woman on June 8. Police said he set fire to the patient's apartment in Neukölln but the blaze went out on its own.

"When he realized this, he allegedly informed a relative of the woman and claimed that he was standing in front of her flat and that nobody was answering his doorbell," police said.

In the following weeks, the suspect allegedly killed two more patients who were 72 and 94 years old.

Investigators did not say anything about a possible motive.

zc/wmr (dpa, AFP, Reuters)