Police are appealing to anyone who may have seen a helicopter in distress near Anna Bay on Friday night to come forward.
The appeal comes as water police vessels continue to comb the waters off Port Stephens in search for the helicopter and the five people on board at the time it went missing.
Police are interested in talking to anyone who may have been in the Anna Bay and Fishermans Bay area between 5pm and 7pm on Friday or may have filmed the helicopter or taken images of it.
Two NSW water police vessels continued to search for debris from the ill-fated helicopter on Monday.
Large seas are hampering the search and any attempt to recover the 1960s-era Bell UH1 that was flying between Brisbane and Sydney on Friday.
Jamie Ogden and Grant Kuhnemann, both from Queensland, Jocelyn Villanueva and Gregory Miller, a married couple from Sydney, and the chopper's pilot and owner David Kerr from Queensland are all believed to have perished when the helicopter disappeared from the Williamtown air traffic control radar at 6.49pm.
The Australian Defence Force confirmed on Sunday that Mr Miller was an employee but he was not on duty at the time of the crash.
"Police were advised of an aircraft fading off the radar about 6.30pm before a search operation was commenced in the vicinity of Anna Bay," a police statement said.
The search, coordinated by the Australian Maritime Safety Authority through the Joint Rescue Coordination Centre, was assisted by officers from the NSW Police Marine Area Command, Port Stephens-Hunter Police District, Westpac Rescue Helicopter, NSW Marine Rescue and other aerial support.
Police said wreckage was spotted by aerial assets off Fingal Head on Saturday before the search was suspended due to the adverse conditions shortly before 1pm.
The tail rotor of the downed helicopter was found by water police about 8.45am.
The Westpac Rescue Helicopter spotted the main airframe less than an hour later, roughly 8 kilometres south of Fingal Bay.
The wreckage sunk before it could be retrieved.
The search recommenced about 7am on Sunday and picked up again on Monday.
Police are urging witnesses to contact Crime Stoppers on 1800 333 000 or nsw.crimestoppers.com.au.