Searches are being carried out in Co Down as part of the investigation into the disappearance of a 25-year-old woman in 2005.
Detectives from the PSNI's Major Investigation Team, along with divers, are searching a number of areas in the Ballyhalbert area, close to where Lisa Dorrian was last seen alive on 27 February 2005.
Detective Superintendent Jason Murphy, who is leading the investigation said he does not believe
Ms Dorrian's murder was pre-planned and that he remains "convinced that a small number of people hold the key" to her disappearance.
The searches are concentrated on a number of lakes at The Clay Pits, close to the caravan park where
Ms Dorrian was last seen alive at a party.
DS Murphy said: "Sixteen years have now passed, but our resolve has not diminished. It is important that we bring the Dorrian family the answers that any grieving family deserves.
"While we want to recover Lisa’s body and allow the Dorrian family to finally lay Lisa to rest we remain determined to bring those who killed her to justice and are also looking for evidence relating to her disappearance."
He said the current search area was "previously considered and work conducted to examine it", but with the development of search techniques and technology, police want to ensure that the "examination of the lakes has been conducted to the necessary extent and to modern day standards."
Searches were also carried out in the area last month, and Ms Dorrian’s family made an emotional return to the site where detectives believe she was killed.
At the time, police said they had received potentially important new information about her disappearance.