Sorry, should have appended a response to this to my previous post.
Again, how are any of us in a position to do this, to be the ones who lay out such a case? I served on a grand jury in my county, and that's when I first learned about confidential informants. Small time stuff, by comparison with this. Drug user caught and as part of his plea, he helps bring in a drug dealer. The thing is, prior to that, I'd never had any direct information about how law enforcement in my county nabbed drug dealers. Since then I've not known the specifics of how they've built any of their cases. Just this one time, I got a glimpse. That's their job, to take what evidence there is of crimes being committed and develop them up to the legal standards needed for warrants, arrests, indictments, convictions.
You're taking the fact that we the public don't have evidence that confidential informants were warranted as grounds for asserting that there wasn't evidence sufficient to warrant such investigation.