United States v. Liu
The government acknowledged at trial that willfulness was the "tricky element" of the case. The instructions that the jury was given on willfulness were:
In order for the defendant to be found guilty of [copyright infringement in violation of 17 U.S.C. § 506(a)(1)(A) and 18 U.S.C. § 2319] the government must prove each of the following elements beyond a reasonable doubt: First, that on a date beginning in 2001 and continuing to on or about July 31, 2003, in the Northern District of California, defendant willfully infringed, that is, without authorization, duplicated, reproduced, or sold compact disks that infringed the copyright belonging to the owners of the works [at issue in this case].
An act is done ‘willfully’ if the act is done knowingly and intentionally, not through ignorance, mistake, or accident.
Can you see why Liu would argue that the jury instructions did not give him a chance to argue that he did not know the copying was infringing?
Arguably based on this text, "without authorization, duplicated..." was meant only to define "infringed" not "willfully infringed", but it is unclear.