I can't fathom why the FBI would have been required to obtain a search warrant in this case because they weren't the ones who searched the servers - the Reykjavik police seized the data under Icelandic law and handed it over to the FBI[1]. According to the FBI's testimony[2], the CAPTCHA on the login page was leaking the site's IP address. The "hacking" that the defense is accusing the FBI of conducting was apparently entering a few invalid logins which caused the CAPTCHA to appear.
As an analogy, if I keep a murder weapon hidden on my property, the police are required to get a search warrant. If I instead keep it at my friend's house, I have no 4th Amendment rights when my friend gives it to the police, especially if the crux my defense is "it wasn't my gun."
The "hacking" was speculation on the defense's part when they filed their motion in August. If you read the motion[1], because the defense didn't yet know how the FBI located the server, Ulbricht's lawyer wrote a long statement speculating that the NSA/DEA was providing the information to the FBI through parallel construction. The defense did not show any proof of their accusation.
A month later, the FBI gave sworn testimony[2] indicating that they found the server because Ulbricht had failed to configure it properly and it was leaking out its actual IP outside of Tor channels. There hasn't been any proof shown that the FBI hacked his server. A number of people have claimed in the past that they came across the actual IP for Silk Road's server as a result of misconfiguration[3][4], so frankly it doesn't surprise me at all that the FBI also found a leak.
Have you actually read [3] and [4]? Based on the comments, the two posts (Made by the same person) were from a notoriously anti-Bitcoin troll on the day that market prices were at an all time high.
I was with you up until I actually read the posts, which I suspect you did not.
I agree [3] looks that way, but [4] certainly doesn't. The thread is filled with people who saw the debugging screens. I think this user's post history is the most informative:
The footnote at the bottom of p3 {1} is hilarious and the referenced law contradicts what the prosecution claim it says.
Paraphrase: 'we said we requested the search using MLAT but then we realised we don't have that agreement with Sweden, so it was probably 2001 CoE Convention on Cybercrime {2} or if it wasn't that then it was comity; we don't really want to say' - presumably they made this up after the fact. I'd be asking for records of the communications.
At Art 15(1) [which is specifically mentioned in the articles on search and seizure] it says:
>"Each Party shall ensure that the establishment, implementation and application of the powers and procedures provided for in this Section are subject to conditions and safeguards provided for under its domestic law, which shall provide for the adequate protection of human rights and liberties, including rights arising pursuant to obligations it has undertaken under the 1950 Council of Europe Convention for the Protection of Human Rights and Fundamental Freedoms, the 1966 United Nations International Covenant on Civil and Political Rights, and other applicable international human rights instruments, and which shall incorporate the principle of proportionality." //
That "each party" means that the state requesting the search and that being requested to do the search, in this case Sweden and USA, have to ensure that they abide by the "safeguards provided for under its domestic law". That means that contrary to what the FBI are claiming if they used this 2001 CoE Convention on Cybercrime to request the search then USA restrictions must be applied to the request, eg the Fourth Amendment.
This {3} recent Cybercrime Convention document reiterates that domestic laws must be applied in certain circumstances (see eg Section 3.2). It specifically relates to Art 32 (unilateral searches of publicly available data) but the language used is such as to reiterate the general principle running through the Convention of the requirement to apply all relevant domestic laws.
This 2001 Convention being used relies on other international laws, I wouldn't be surprised if the cited UN convention also means that a court must be involved in the issue of the request. The Art 15(2) ibid appears to say that an independent or judicial review of the request is required.
tl;dr if the footnote on p3 is correct and {2} was used then, just as for the Pennsylvannia server the USA authorities needed to satisfy USA domestic law before requesting the Swedish authorities search and imaged the server there. If they would have needed a court issued warrant if that server were in USA then they still needed one to make the request under the Cybercrime Convention.
As an analogy, if I keep a murder weapon hidden on my property, the police are required to get a search warrant. If I instead keep it at my friend's house, I have no 4th Amendment rights when my friend gives it to the police, especially if the crux my defense is "it wasn't my gun."
[1] http://www.scribd.com/doc/238796613/Silk-Road-Prosecution-4t... (page 12)
[2] http://www.scribd.com/doc/238844570/FBI-Explanation-of-Silk-... (page 3)