I just finished watching the second series last night (Summer didn't seem like the right time to watch it). Perhaps I'm rose tinting my memories of the first series, but I was mildly disappointed with this one. It makes sense for the story that they would do fewer interviews this time, but without those it's basically just another police procedural.
Also, it might have been a bang on impersonation of Manson, but all I could see was a hairy Dewey Crowe. On a related note; do they just not care about the agents swearing on tape any more? Ford saying 'cunts' in the first series wound up getting their boss fired (not directly, I know) but Tench swearing at Manson caused no blowback at all. Also also, it was rather contrived that Tench's kid was up to some bad business at just the right time for Manson to give his "your children" speech.
It's still good and I'll certainly be watching a third series, but maybe without as much anticipation.