Interpol. They do a lots of this investigation, because it is international and crosses so many borders.
Uk, US, Mexico and the Philippines are all members of interpol. If uou think back to all the high profile investigations, operation ORE for example, started in the USA, expanded worldwide. Tracking down customers of a website I think, where images were downloaded from.
It's an international crime, and it has international forces working on it. That is why it is so odd, to me, that this guy was apparently being investigated, but he was changing countries, shipping boxes of stuff around the world, and was never caught. Esp if he was downloading.