Unfortunately I don't think they are ever going to catch Froome unless they set him up like they did Landis.
I will elaborate on this. When Floyd Landis was in Melbourne in 2010 for the World Championships, I looked after him for the week. I had dinner with him and other every week. I also did an interview with him which was published. Anyway, the stuff he was telling me was quite insightful. I knew at that stage who the riders were that testified against Lance Armstrong. Yet it only came out to the media and everyone else in 2012. So it was old news to me when the story broke.
Anyway, Landis was telling me how after a Tour de France stage a team mate would hand him a blood bag and he would put it in his jersey and ride back to the hotel and no one would notice. He also told me a lot of stuff and he and everyone else did and how open everyone was.
Up until 2009 (this was confirmed by more than one rider) all the cyclists would talk about what drugs they were on and what they were doing during stages. Ever since people started testing positive, everyone has kept quiet about what they are on because they don't trust anyone and don't want to get caught. To this day nothing has changed. No one will be talking to other riders about this because the mood is somewhat dull. Basically this is common knowledge, cyclists have a code where that if you get caught, you never ever break omerta. You wear your punishment and you'll be signed again after your ban. If you talk and dob people in, you will never get a professional contract again. So that's why riders don't talk when they are caught.
Landis was also set up that year he won because he told me that he was on EPO, HGH and everything under the sun. He was tested for those things all throughout the tour and they all turned up negative. The only thing he wasn't on was testosterone and he 'got caught' for a positive testosterone test. Unless the other things he was on raised his testosterone level, it doesn't make sense that all drug tests turned back negative and the thing he tested positive for was the only thing he wasn't on. It was quite insightful.