A German Bundeswehr soldier is suspected of shooting dead four people in the Lower Saxony district of Rotenburg, before turning himself in, the police and prosecution announced on Friday.
A child is among the dead, who were found earlier in the day.
There were two crime scenes - one in a detached house in Westervesede in the municipality of Scheeßel and one in Bothel in the district of Rotenburg.
The suspected perpetrator turned himself in after the attack on Thursday night and was arrested, the investigators said.
Police said a domestic issue "cannot be ruled out" as a motive for the crime.
A large contingent of police officers has been deployed.
