Professor John Jones described to Nottingham Crown Court how Julie Dart was knocked unconscious and then strangled, before her naked body was dumped in a field.
He added that she had been dead for probably eight to 10 days and possibly kept in a wheelie bin before being dumped, wrapped in a cotton sheet and trussed up tightly in the foetal position.
Her body was found in a field at Eastham, near Grantham, Lincolnshire, last July after police received a ransom demand of pounds 140,000 for her release.
Michael Sams, 51, of Barrel Hill Road, Sutton on Trent, Nottinghamshire, has admitted kidnapping 26-year-old Stephanie Slater, a Birmingham estate agent, falsely imprisoning her and demanding pounds 175,000 with menaces. But he has denied kidnapping and murdering Miss Dart, from Leeds, twice demanding pounds 140,000 with menaces from the police, and demanding pounds 200,000 with menaces from British Rail.
Professor Jones described how he was called to Eastham in July, where he saw Miss Dart's body wrapped in a pink and white sheet. He described two injuries to the skull and said the second had caused a fracture and substantial bleeding and could have been the result of a blow from a hammer or another blunt instrument.
But Professor Jones said the blows to the head had not caused death.
There was bruising to the neck, which he said was due to a ligature and there was also a mark around her right ankle which suggested she had been held by a chain or coarse rope. Death was caused by 'compression of the neck and head injuries', he said.
The case continues today.