The concrete evidence could still be a photo in the scenario of her being killed in 5A, CB might have chosen to take photos of the corpse afterwards and maybe other sickening acts before diposing of her.
As the for Russian link, there's no reason to think they have anything more to do with it than any of the other thousand theories touted in the press over the last 3 months. All the people we've heard as possible accomplices etc, they can't all be involved in this crime. It's clear LE have being trying to track every known associate of CB to see if they know anything that can help. My guess is that it's just another instance of that.
The job he had to do? That apparent quote is a fourth hand account. CB said something to his ex. That ex then relayed her interpretation of what she recalls him saying to a friend. That friends tells his interpretation of this to a tabloid. That tabloid writes a piece sensationalising as much as possible to sell papers. I don't know how much reliability can be placed in the accuracy of it to be honest.
However, even if it was said as quoted, a planned burglary still fits the description of a horrible job. I do wonder why, if he was planning to abduct a small child, something that's obviously going to become major news, why he'd give his girlfriend a heads up on it.