If he has a habit of masking himself and his victims, then given the sort of people he was probably sharing such videos with, I'm not suprised it could potentially take years to get to the point where the video could be found by the police, and years more until they can actually do something about it.
Add some disguises and crappy 2007 video and it could be almost impossible to be sure who is in the video
There's a website run by (I want to say the FBI but it's probably not them) which has images taken from videos of child abuse. Pictures on the walls, unusually patterned curtains, that sort of thing. They have asked the public to look and see if they recognise anything and to contact them if so.
I do wonder if they've had a video for quite some time, have long suspected that MM was in it, but couldn't be sure, until something else has recently emerged that means it likely is her. Obviously that's just speculation and we'll never know because why should we. But I do wonder if there's been something simmering away in the background. That would explain the vast amounts of time, money and support given to finding MM- I don't begrudge it by the way, but it has been a lot more than for other missing children. If they end up cracking some massive paedophile ring during an operation that has been years in the making, and could potentially involve many more children/people in positions of power, well it would make sense.