It wasn't like the FBI was already behind the curve. When they searched and seized the computers of an Anon IRC Admin [https://www.infosecisland.com/blogview/11586-FBI-Acts-on-Another-Anonymous-DDoS-Search-Warrant.html] just a few days ago. Or when they stupidly admitted to the complicity of their own members arrested under suspicion as they declared "war" on the United Kingdom's government. [https://www.infosecisland.com/blogview/11407-Anonymous-Calls-UK-Arrests-a-Declaration-of-War.html] Or when they got legitimate activists arrested and likely killed in Tunisia [https://www.infosecisland.com/blogview/10773-OperationTunisia-Backfires-Activists-Rounded-Up.html] because pissing off dictatorships that are more than happy to pull the trigger on their own citizens sounds like a great plan.
Their ineffectual attempts in Egypt [https://www.infosecisland.com/blogview/11383-Anonymous-DDoS-Targets-Egyptian-Government-Sites-.html] and Zimbabwe.
Now they're adding identity theft (not that some of their members haven't already taken liberty with data lifted from Visa and Master Card), obstruction of justice, and a host of other crimes when they are caught. Not to mention if people are all complicit in the same crime as a group. (For obstruction of justice, interfering with a criminal investigation, interference with commerce, bank fraud, identity theft, etc.) Let us not forget that particularly their DDoSing crimes come with a 7,000 dollar fine and up to 10 years in prison. Each. Not to mention significant civil liability from all those companies (Visa, Mastercard, Amazon, Bank of America, PostFinance, etc) that they've wronged.
I suppose you can say they won't find all of them, but they don't need to. They may not be a coherent organization, but under the law it's likely that they'll be treated as one. Plus it's not like these governments aren't used to attempts at intimidation. It's not like they don't have the ability to strike back. Every attack Anonymous undertakes (whether under the banner of group or individual it doesn't matter so long as they're using the name "Anonymous") is going to lead the authorities back to them. Their "declaration of war" shows them to be stupidly naive about not only the law, but their understandings of protests (sit-ins can get you arrested for trespassing, and peaceful protesters can be arrested if A) they fail to get a permit and B) if they attempt to disrupt the business of the organization in question, you can protest someone going into Starbucks, you cannot however STOP THEM FROM ENTERING), and their own rights afforded to them under the constitution.
Anonymous is going to be charged as a group. That means if one individual was part of the attack, they're most likely going to have ALL the attacks and everything Anonymous has ever done that's illegal dumped on their heads. Now a good lawyer should be able to talk that down for them, but that's where this starts for the accused.
I'd advise them to stop now, but that won't happen. Unfortunately for Anon governments, law enforcement agencies, and security firms are used to intimidation tactics and death threats. They don't bother them and the threats of "hacktivists" (though they will surely be taken seriously) will be treated the way they deal with all terrorists, cyber or otherwise. The U.S (and I assume the U.K) does not negotiate with terrorists. All the bullying attempts in the world ain't gonna make them stop the investigation.