The wife of a wealthy Norwegian businessman who disappeared nearly eight months ago was probably killed and the murder made to look like a kidnapping, police have said.

Anne-Elisabeth Hagen, whose husband, Tom Hagen, is a real estate investor and energy magnate, went missing from their home in Lørenskog, near Oslo, on 31 October.

The Verdens Gang daily reported that the presumed abductors had demanded €9m (£8m) in the cryptocurrency Monero, a digital cash system that is especially hard to trace. A ransom note had been found at the couple’s home. Police at the time refused to confirm the sum but said they had advised the family not to pay.

Online contacts with the presumed kidnappers earlier in the investigation were unable to confirm that those people were holding Hagen, 68, or that she was still alive.

Tommy Brøske, the lead investigator, told a news conference: “As a result, our main hypothesis has been modified – Anne-Elisabeth was killed. There may have been an attempt to disguise the murder as a kidnapping.”.

He added that the supposed abductors’ lack of a desire to “bank the ransom” was one of the other key factors behind the conclusion. He declined to state whether police had any suspects in the case.

The family’s lawyer, Svein Holden, told reporters he viewed the crime as a “kidnapping that turned into a possible murder”.

Tom Hagen, in his late 60s, has an estimated fortune of €174m, according to the magazine Kapital.