IIRC, this would not be the first time a tax protestor has been "linked" with a child-related crime. I remain suspicious of the federales.
Putting on my tin foil hat here:
All the cops have to do is email you kiddie porn, then they can break into your house, confiscate your computer, and arrest you when they find the evidence. Heck, the could mass email it out and arrest EVERYONE.
That was my first thought, too. How convenient for them to find this on his computer which was in their possession. How can we be sure the IRS didn't download it?