I'm not surprised that Dr. Kogan is not co-operating. Let's assume Dr. Kogan has gone and taken this data. We would call this stealing, when you go in through the back door, take something that doesn't belong to you, and it's against the rules. I'm going to say Dr. Kogan has stolen this information.
The question becomes, why would Mr. Steve Bannon go all the way from the United States to Europe, to the U.K., and engage SCL and help start Cambridge Analytica? Did they have any specific abilities, or was it simply that they had access to this data?
Have you spoken to Mr. Bannon? Are you planning to speak to him as part of your investigation?