Officers from the Major Crime Investigation Team are continuing their search in and around a pond in Ramsbury, being expected to drain it tomorrow.
A flurry of activity at the end of last week saw police pull two boots Sian O’Callaghan was wearing the night she died in March 2011, and a single-barrelled shotgun from a the pond a few miles outside the village.
Wiltshire Police said this afternoon that the specialist dive team from Avon and Somerset Police will continue their efforts at the scene tomorrow when they will drain the pond and conduct further searches.
Searches by police officers and cadaver dogs are also continuing.
Hilldrop Lane remains closed and diversions are in place.
A team of 25 to 30 officers, including divers from Avon and Somerset Police and cadaver dogs from South Wales Police, were dispatched to the scene last week after lead investigator Detective Chief Inspector Sean Memory made the find along with a colleague.
A police spokesman yesterday confirmed forensic tests on the shotgun recovered from the pond would now take place, while any serial number on the rusted weapon would be run through the police database of licensed gunholders.
She said: “The shotgun will have to be sent away for analysis and if it has serial numbers, we will be checking on our database.
"We are keeping an open mind as to whether it is connected to the enquiry.
“Nothing else has been recovered since Friday.”
The developments come after former Detective Superintendent Steve Fulcher resigned from his position at the force.
It followed disciplinary proceedings that found him guilty of misconduct for ignoring force orders and breaching the Police and Criminal Evidence Act when questioning Sian’s killer Christopher Halliwell, of Nythe.
His actions meant a second charge of murder against the mini-cab driver, 50, for the killing of Becky Godden-Edwards was withdrawn after a judge ruled vital evidence inadmissible.
Anyone with any information that could be of interest to the enquiry should contact Wiltshire Police on 101 or Crimestoppers anonymously.