Dunno.. there are many roads possible that could lead the police to more dirt...
- They will already have access to Spike's financial records which could turn up other transactions.. including things Brett possibly hasn't acknowledged. If so, then they will have more cause to investigate him more.
- Someone can flip... including Spikes. Whose to say he doesn't know others doing the same thing with mr. finley? If so, the prosecution will have more bartering power to give up on spikes to chase the bigger fish.
- You also now have big public figures involved, that would love to paint themselves as the victim and not the only one.. so if they have other leads of who might be socializing and discussing these buys with mr finley... you can bet those high profile people would be eager to name names to take the focus off them as the top of the pyramid.
Once they have their foot in the door with real evidence of crimes involving someone, the doors open quickly to expose more links and associates. Especially when the people are sloppy.
Clearly before the interview the police had knowledge, but not the concrete evidence in hand... but once they got the phone and more physical evidence... the doors swing open for more searches.
They've been slow to prosecute because it looks like they are still aiming bigger...