Police are searching remote farmland for the body of Janet Brown, a TV extra who went missing eight years ago before she could claim her parents' £1m estate.
There has been no confirmed sighting of the then 45-year-od, who lived in the Lowgate area of Hexham, Northumberland since June 2005.
Northumbria Police arrested a 59-year-old Tynedale man on suspicion of murder in December, and he was bailed pending further inquiries.
Ms Brown loved to travel and friends were not concerned when she went missing.
However extensive inquiries around the world, including in Thailand, have drawn a blank and now police feel sure she has been murdered.
Previously, the arrested man was held on suspicion of fraud when concerns were raised about allegedly suspicious bank activity relating to the account of her dead parents, reported to be worth £1m.
Ms Brown, who worked on the TV show Distant Shores, never made a claim for her inheritance after they died.
Officers were scouring a farm near Sparty Lea, south west of Hexham, in the remote North Pennines.
Wearing fluorescent jackets, search specialists were seen at the 40-acre farm, which has not been worked for several years, dismantling a dry stone wall. They also have a digger and dump truck available to use.
It was expected the search could last for several weeks. The force has drafted in experts in archaeology and geophysicists.
Detective chief inspector Nicola Musgrove, speaking outside Hexham police station, said: "The police investigation commenced in 2009 after a report in relation to irregularities in the parents' bank account.
"As a result of that we started looking for Janet Brown and after extensive enquiries to try to establish where she was, we've come to a point that we believe that she's dead and this is now being treated as a murder inquiry.
"It has been a really difficult investigation.
"Since 2009 we've been trying to find some evidence that Janet Brown was still alive but I'm now satisfied that she is dead.
"Her parents are both dead and there is an estate but she has never claimed the estate.
The detective added: "These searches will be detailed and it is not clear what, if anything, they will reveal.
"That's why we still need the public to get in touch if they have any information at all about Janet Brown's whereabouts over recent years.
"Any information, no matter how trivial people think it is, could prove vital."
Temporary chief superintendent Dianne Winship, from Northumberland Area Command, said: "While we appreciate people may well be concerned by these developments I'd stress there is no risk to the general public and this is a long running and historic case.
"I'd also like to reassure the people of Tynedale that any disruption will be kept to an absolute minimum and there won't be any change to day-to-day policing in the area."
Anyone with information should call 101 or Crimestoppers on 0800 555 111.