From what I have seen of Lulzsec it is a fairly insulated organization. They seem to be based upon a system made up of three tiers. Each placed within a hierarchy. Which would be Leadership, Initiated, and Uninitiated. The Leadership is insulated from the Initiated, and the Initiated are insulated from the Uninitiated. None of these groups use the same forums, chat rooms, or websites. The Uninitiated if you haven't figured it out yet aren't actually in the group. They are pleading the case for their inclusion in a public setting. Which means they may have a couple initiated members that are watching these sites looking for candidates. Anyone who has any real access is already safely removed from the bustle, and even the initiated that are watching. Probably aren't actively engaging, but are instead buried under twenty proxies getting severely delayed transcripts.
Basically once one of the Uninitiated caught wind that they were being raided, and screamed out to the mass. The Initiated members of Lulzsec had ample time to leave before there was a chance to trace them, and lets face it all, but one guy was able to get away. Yeah a room full of people, and they were only able to grab one of them. Even then it was probably the weakest of the lot. Good job Cops you nabbed the guy in a wheel chair. Seriously Lulzsec has a lot to laugh about with this. Nobody important got caught, and only one guy was even nabbed. The guy who probably also knows jack shit.
Who knows he could have been a journalist, a sight seer, a student, or someone who works in security looking for pointers. This is something that the police themselves actually practice. They go to places frequented by criminal groups to find out how they do their crimes.
Anyway this is a pretty sophisticated group. The best option for law enforcement is to use rewards, undercover operatives, and well placed traps. Offer a good sized reward, and someone high up might be convinced to work as a double agent for them. Getting some guys on the inside would also be a good idea. Being able to predict a attack might allow them to catch the hackers unawares. Raiding a fan club is simply uninspired. No sophisticated gang has been brought down by that knucklehead shit.