Detectives investigating the Coleraine dentist Colin Howell are searching a lake and the grounds of a house in Castlerock, County Londonderry.
Mr Howell, 50, is charged with the murder of his wife and his lover's husband, RUC officer Trevor Buchanan.
Police recently asked the courts for permission to interview Mr Howell about other matters.
However, officers have indicated that they are not searching the property for human remains.
The bodies of Leslie Howell and Trevor Buchanan were found in a fume-filled car in Castlerock on 19 May 1991.
Their deaths were originally thought to be suicide.
Mr Buchanan's former wife, Hazel Stewart, 46, is jointly charged with the murders. She is currently out on bail.
Mr Howell has been in prison since February.