Showing that someone "is up to no good" has always
been more difficult than proving they actually did something
wrong. This has been a problem for accusors since the dawn
of time. The fact that justice can be difficult is no good
excuse to take shortcuts with the process.
On the basis of the briefs, it looks like the law professors have a better case based on the language of the statute. But I have to say that I don't see this as a case of some vague "up to no good" standard. If the distribution actually took place, there was infringement. If the distribution didn't take place, there was no point in making the files available.
It would be like hiding a camera in the girls' locker room, then arguing that no invasion of privacy occurred unless someone was actually watching the monitor while the girls were in the shower. It's hard to prove when someone was watching, but there's no point in putting the camera there unless you want to watch.