Slushpool helped me with data and timestamps. I was able to follow the bogus login to a relay system in Budapest. The relay system was accessed from a VPN service. I have been in contact with the owner of the VPN service. He will not release personal info on the account holder who created the VPN account. Although the owner has not said so, I believe that the VPN hardware is physically located in the UK.
In short...if the VPN business owner were willing, I could obtain personal info on the owner of a VPN account (one of several) that was involved in the hack that stole my bitcoin. (Missing bitcoin is currently worth about $7200.00 USD as I type this message.)
So...Slushpool is/was innocent. It was not an inside theft. For various reasons...too many details to write here...the bitcoin theft appears to have been enabled by one or more of the Yahoo password and personal info leaks. (Among other things, one of my Yahoo email accounts had been programmed to block messages from several Slushpool email addresses...)
Can anyone recommend a police or cybercrime agency in the UK, that would have the legal right to demand user info from the VPN service?
Thanks! tfEagle