Police are said to be working on the theory that Miss Yeates, 25, was killed inside the flat, put inside the bag then transported into a vehicle where she might have been left for several days.
A source told the Sun newspaper: “Information has come to light which is set to take the inquiry into a significant, and different, direction.
“The investigation team believe they have made a very important breakthrough.”
Miss Yeates, 25, was found dead on Christmas Day, eight days after going missing from her home in the Clifton area of Bristol.
Her body was found next to a country road in Failand, three miles from where she lived.
A post-mortem examination revealed she had been strangled.
Miss Yeates, who was originally from Ampfield in Hampshire, was reported missing by her 27-year-old boyfriend Greg Reardon on 19 December when he returned to their home after a weekend away visiting family in Sheffield.