If it were premeditated, they would have left their cell phones on and at Raf's place. The problem with Rudy is that there is zero communication between him and the pair, except as pure, unalloyed conjecture.
Knox had met Guede several times prior to the murder: in the pubs, at a party, and in the plaza. Each time, there was no communication between the pair prior to having interactions together, such as going together to a party. We should not forget that Knox made fast friends with fellow illegal drug abusers like Sollecito and Guede.