I didn't see it listed in the story. What Manga was it, and what did the frames contain? How did they know what was in it?
You see this kind of thing all the time over the Second Amendment, but i'm leaning towards something a bit less serious here (for everyone except the poor guy who it's happening to, that is).
If the manga contained images that would qualify as child pornography, either on the state or federal levels, the guy is toast. In fact, I'm leaning in that direction. Whether that image meets the definition properly, as opposed to say Ropponmatsu II (which could even be argued at times), is the defining issue. Even if he didn't know it was in the manga, he's still responsible for possessing it.
Lets be perfectly honest here. The facts aren't being reported in full. Until you know the full scope of the details, it's pointless to worry about infringement of rights.
And for any of you with any huffing about what the cops can and cannot nail you for... If you have any ROMS or CD images without the originals, unpaid-for MP3's, or VHS recorded NFL games, you're breaking the law, and can be nailed for it if the cops search your home for anything else. Ignorance of the law is not a defense.
My guess is the guy was reading it in a place where someone got offended at the content, they called the cops, likely saying it's kiddie porn, and no judge will refuse a warrant for kiddie porn.
Again, the guy's defense depends on the definition of the content. This has nothing to do with "objectionable material" as it's normally dealt with in American released comics or manga.
You can't show breaking glass in a comic that is released in Canada, or so I'm told. If such a comic were imported via individual purchase, rather than distribution, the law has been broken, and you can be held legally responsible. It's just the way import laws work.