While we, the public, don't have all the details and can never have all the details, we are told he had plans for shooting and bombing police at his house pre-dating the recent Baton Rouge and Minnesota shootings by cops. This doesn't prove he didn't actively coordinate with BLM, but it suggests that he was planning a more well conceived plan at a later date, but moved it forward after the recent shootings.
It takes no coordination with the leaders of a public protest to do what the shooter did. And if the shooter did try to coordinate with BLM organizers he sets himself up to being revealed to the police as it would get the BLM in deep shit if it were found out they had any involvement with a sniper taking out police. Certainly it would be folly for BLM to somehow sign off on having a sniper shoot police at a rally they organized.
There is absolutely no evidence to lead to a tie between the shooter and BLM other than both entities being upset about the same situation. Of course the BLM movement, if you want to call it that, could add some fuel to a persons fire. But you can say the same for any opinionated speech.
I think BLM and many SJW types shoot themselves in the foot with their rhetoric and I don't want to be associated with them personally, but without some evidence I will not jump to the more absurd conclusion just because I don't like them, and I suggest you don't either.
There are other topics we can spend our time with that are not complete speculation.