Tayside Police crime scene investigation officers are continuing their probe at a house in Balunie Avenue in Dundee into “historical incidents”.
It is understood the inquiry concerns incidents dating back at least 20 years, but the nature of the crimes remains unclear.
Officers carried bags to rear of the property where a blue forensic investigation tent was set up for the second day in a row on Thursday.
Police confirmed the single property remains the focus of investigations but more addresses may come under the microscope in the coming days.
A spokesman for the force said door-to-door inquiries are continuing to establish whether anyone has information that could be of assistance.
“Investigations are at a very early stage and it is anticipated that they will be ongoing for some time. During the course of the inquiry one or more addresses may become of interest to Tayside Police.
“As stated, inquiries are at a very early stage and it is not appropriate to comment any further at this time.”
A large police presence descended on the street first thing on Monday as the operation got under way.
