Even aside from all the (many) problems in regards to Holmes' acquisition of Moriarty's notebook, there's another issue. The whole idea behind sending the notebook to England was so that Lestrade could seize Moriarty's assets. They had no valid reason to arrest him, and taking his money would at least slow him down. (It's a little odd that such an intelligent man would have so much of his net worth just lying around in safety deposit boxes rather than investing more of that cash somehow, but we'll let that slide.) The real problem is that Scotland Yard has no valid reason to keep said valuables, either. Moriarty is, legally, an upstanding, law-abiding citizen. All he has to do is complain to the British government that his property has been illegally seized, and Scotland Yard has to give all it back.