The warrant covers "any communications that that might be found in Mrs. Hudson and Mrs. Flanagan’s home related to “the acquisition of firearms or accessories.”
Likely the term "communications" includes written communications, in which case they would have had to seize all written records in the home, unless they wanted search though all of them on-site. I doubt agents are experts in filtering documents during a raid.
Furthermore, if the police find something not related to the search warrant but criminal in nature (like a dead body or possibly stolen records) they can seize them, too.
Except, at least according to Hudson's story, they were very specific and limited in the papers they took. They knew what they were looking for, it wasn't about guns, and they found it.
Likely the term "communications" includes written communications, in which case they would have had to seize all written records in the home, unless they wanted search though all of them on-site. I doubt agents are experts in filtering documents during a raid.
Furthermore, if the police find something not related to the search warrant but criminal in nature (like a dead body or possibly stolen records) they can seize them, too.