Parallel reconstruction is not so easy when the case is already at trial as you can bet the defendant will not be doing whatever it is law enforcement need to now find evidence of. Time machines are still not available.
Ignorance like this is a large part of the problem with the world.
They could hope the ∆ was using BT and had their IP logged for downloading copyrighted material. Then maybe request a warrant for their computer that way but that seems like a stretch.