“A family member has been arrested on suspicion of murder. This is a tragic family situation,” police spokesperson Stefan Marcopoulos told the TT news agency.
According to the Aftonbladet newspaper, it is the boys’ mother who is being held in connection with their deaths.
The brothers were found in the water near a dock, and their clothes were also discovered nearby.
The boys’ father reported the disappearance late Sunday evening, and police initiated a comprehensive search and rescue with sniffer dogs, helicopter and divers.
The boys were reportedly down by the water’s edge near Munkholmen in Sigtuna.
While their clothes were found early in the search, their bodies weren’t located until Monday afternoon.
Speaking with Aftonbladet, Marcopoulos explained that the it remains unclear whether or not the boys were alone near the water or whether they had been accompanied by their mother.
“Interviews are underway with both the boys’ mother and father,” he told the newspaper.
According to police, the boys bodies show signs of injuries indicating that a crime was committed.