Earlier someone mentioned Occam's Razor, which is something I also tend to believe in.
Of course there could be other people involved, or underworld connections, or any number of other things.
But to me, the simplest "Occam's Razor" explanation is that the two apparently elderly victims were known to the suspect, who was perhaps a lodger or something like that. He killed them for whatever reason, and in his desperation to dispose of them, he packed them into suitcases and took them to Bristol--where they had been planning to go on holiday.
If they were found and the police later came to speak to him, he could say something like, "They never came back from their holiday, I don't know what happened!"