The murder trial revealed a number of puzzles within the case, including the fact that Yeates was found without one of her socks, which was never recovered.

Another mystery is that Yeates bought a pizza  as she walked home on the night of her killing, but neither the pizza nor its box were found at the flat, and Yeates had not eaten it.

Detective Chief Inspector Phil Jones, who led the investigation that ended in Tabak being jailed for life last week, said of the sock: “I felt it could have been significant in that it was a trophy.

“I think he took the sock and the pizza because he was linked to those items evidentially. No other trace of him was found in the flat.”

Keeping a personal item belonging to a victim as a trophy is a common trait among killers.

In court, Tabak claimed that the sock fell off in Yeates’ flat and that he put it in a municipal bin.

He also said that he dumped the pizza and its box in a bin. He admitted that he had eaten a pizza on the night of the murder, but insisted that the pizza he ate was not the one that Yeates had bought.

However, police sifted through 293 tons of rubbish during the murder investigation and never recovered the sock or the pizza.

Police suspect that Tabak – who, it was revealed after the trial, would watch porn videos of women being strangled – ate the pizza after he killed the 25-year-old landscape architect.

DCI Jones described Tabak as a “cold and calculating” killer.

He added that the body may never have been found if Tabak had successfully dumped his dead victim in a quarry as he had planned.

However, because Tabak didn’t succeed in throwing the body over a fence and into the quarry, he left the body by the side of the road. It was found eight days later by a couple walking their dog on Christmas Day.

Police are puzzled as to why the 33-year-old, 6ft 4in Dutchman failed to heave the body of 5ft 4in Yeates over the wall.

Tabak claimed in court that he lacked the strength, and so covered her body with leaves by the side of the road instead.