I've heard more than once on Sky News that a man in a police uniform, and who looked like the island shooter, was seen leaving the are of the downtown bombing. That does raise the incredible possibility that the same guy perpetrated both acts. I don't know the time frames.
They just said in the press conference with the PM that the island shooter was Norwegian (no mention of any other affiliation).
Agreed, time frames, distance, multiple vehicles (one at bomb site, then transport to island location).
Still much to find and assess .... imho