Here's a Snowden video in which he explains it (scroll to the bottom of the article): http://politiken.dk/udland/ECE2108923/usas-spioner-overvaage...
The other problem is your worldview is not falsifiable. Everything Snowden says is true to you and everything Google says is false because Snowden said they would lie about it.
The Guardian and every other major news outlet seemed to think his evidence was compelling.
Not sure what makes you think that journalists are a legitimate authority to make appeals to.
Snowden/Guardian: NSA is doing X Govt/NSA: We are not doing X Snowden/Guardian: Here are some slide/proof Govt/NSA: Ok we are doing X, but it's for your own good.
Rinse and repeat each fortnight.
So each denial means less and less, and tips believability towards Snowden even where the proof is inconclusive in some cases.