The short story is that SCOTUS decided that the warrant was no good & therefore the search executed was illegal, & further that the agent in charge of the search was not protected by the (overly broad) immunity given to most agents of the government when acting on the government's behalf.
I'd like to do a detailed post on the decision (particularly the dissents) but I'm just not sure if I'll get around to it anytime soon. So in case I don't you have the decision as well as the warrant in question if this type of thing interests you.
I will point out that the warrant was served by a joint force of local & federal agents with the ATF leading the search. Also the search turned up nothing. Seems the "reliable informant" that the ATF got its info from wasn't that reliable after all. Typically the ATF will threaten someone with prosecution over a bogus & trivial matter (then again all federal firearms laws are bogus & trivial) but offer him/her a deal: they'll graciously not prosecute if he/she will just
But as I said, I'll try to get around to a more in depth post on this if I can. In the meantime thanks to KABA.com for obtaining the documents & making them linkable.