Great overall post. I disagree on this particular part of it just because I feel confident that something within this realm would've been required, at a minimum, for a federal judge to sign off on that search warrant. Possessing any or all of these things in and of themselves would not result in an arrest anyway.
What they would need for an arrest is physical evidence showing that the suspect was in the home at the time of the abduction, or physical evidence that the victim was with him after the abduction. That would be DNA, fingerprints, or a clear video/image of him in the home or entering the home around that time and then leaving the home with the victim, or video or other evidence of him with the victim after the crime. Both DNA and fingerprints, while compelling, would need quite a bit of supporting evidence (i.e. the evidence they used for the search warrant). With electronic evidence only, they could just show that he was in the vicinity around that time.
This then (partially) challenges another thing you outlined, because even if they could demonstrate within a reasonable doubt that his IP address was used to create the ransom email and to open/monitor the Bitcoin account, it wouldn't be enough to make an arrest. Enough for a search warrant, yes, but not an arrest. They would need physical proof that he was using the IP at that time and for that purpose, or at a minimum be able to exclude everyone else with access to that IP.
To me (at least how I'm thinking today

), with no new noise, no new movement, and all press conferences cancelled after that last raid, it suggests LE is confident they found their perp(s) and are waiting for the final confirming pieces of evidence to fall into place. Remember - LE could absolutely know who did this without being able to prove who did this. The last part requires some meticulous evidence synthesis and analysis, and no room left for doubt.
As we know all too well at times, no jury will convict (anymore) based solely on a chest badge and raised right hand. They have to spoon feed convictions nowadays. A tall order, but that's what they signed up for.
JMO.