There is no source on that because it isn't true[1].
Ulbricht was found via the server - all evidence that came as a result of that (including the laptop) would have been dismissed if a 4th amendment appeal was successful.
The only evidence found outside of the server chain was the posts to the Shroomery and Bitcointalk - and as the link in grandparent comment points out, this is not sufficient probable cause for a search warrant (and a search warrant on the Gmail in any case would still not have linked Ulbricht to DPR sufficiently)
[1] right in the second paragraph of article linked in grandparent comment:
> The arrest of Ross Ulbricht got its start when the FBI somehow discovered the real location of the Silk Road server in Iceland.
and
> Every shred of evidence except for two “hey, I found this site” posts derives solely from the server seizure.
a) market cap is meaningless for currencies - you want to look at transaction volume
b) you're comparing apples and oranges - the market cap for USD is not the total value of printed currency
c) btc transaction volume currently averages about $65M per day, which is $23.7B p.a - about 4x the size of the Apple App Store and about one-eighth of PayPal's $180B p.a and larger than all but the top 3-4 online payment providers
d) it is still very, very early days for btc. it's goal is to not replace PayPal, but to have these payment gateways build on top of it.
e) there are dozens of blockchain based applications currently in design, draft, development, beta test etc.
f) the current implementation of btc for payments is horrible yet despite that it has established itself as a viable payment backend with a non-insignificant portion of the market
g) comparing bitcoin with any fiat currency, let alone the worlds major reserve currency, is very flattering
https://twitter.com/sarahjeong/status/555821164661321728