The original still has some importance for evidentiary procedure. Copies are good for the evidence on them, so long as you can authenticate them. The authentication process, therefore, is so much easier if you have the actual laptop and a clear record of each moment it changed hands. It could take days in court to describe before a jury why/how a copy is just as good as the original for the sake of prosecution. On top of that, they could probably snag some DNA off it for whatever reason.