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."
Detectives are working on the bag theory because they have found no signs of dragging on Miss Yeates' body.
Officers disclosed earlier in the week that she had not eaten the pizza she had bought in the hours before she was strangled.