Here is the full text of the grand jury indictment:
An indictment against Casey E. Frederiksen states, "In or about July 2005, in the Northern District of Iowa, defendant Casey E. Frederiksen, knowingly possessed and attempted to possess images of minors engaged in sexually explicit conduct, said images having been produced using materials that had been shipped and transported in interstate and foreign commerce, namely, a computer hard drive, which was manufactured outside the state of Iowa. This in violation of Title 18, United States Code, Section 2252A (a) (5)(B).
According to the U.S. code it could have been obtained via a computer so it didn't have to be mailed. could have been emailed or downloaded
(B) knowingly possesses any book, magazine, periodical, film,
videotape, computer disk, or any other material that contains
an image of child pornography that has been mailed, or shipped
or transported in interstate or foreign commerce by any means,
including by computer, or that was produced using materials
that have been mailed, or shipped or transported in interstate
or foreign commerce by any means, including by computer,
shall be punished as provided in subsection (b).