I, for one, do not believe him. At all. I believe he knew. And I have my own reasons for believing that, so it's IMO but not, IMO, mere speculation.
BM claims he didn't know, because that makes him the even more obvious murderer. But he said things to people (who then repeated them on youtube and elsewhere, before basically going into hiding) that make me seriously doubt that he learned from the FBI. The things that BM said were later corroborated by JL. There was a particular statement he made about Suzanne and "some man" to one of his co-workers (perhaps MG). MG, at any rate, departed CO and said it was because of fear of Barry. MG and Barry's closeness was apparently notable, as MG said many people thought they were having an affair, which she denied - but she did say they were good friends/close work associates. She was on the list of witnesses for his future trial, when he was indicted.
If you want to go down a rabbit hole, you can go back through the scant MSM stories on the time that Barry followed Suzanne to Florida, I believe it was. She was going there to "visit family," but he knew she was also meeting up with JL (who admitted he went to Florida too). This information came from Suzanne's best friend, IIRC. It's in the threads here.
So Suzanne went to Florida, and then Barry (without telling her) took a flight to Florida. During that trip, she met up with JL, IIRC. And I believe BM knew that from that time onward.
I believe Suzanne's friend and not Barry.
Obviously, this is a matter of our personal interpretation of the various accounts. ICBW, but am interested to see if any of the other "old timers" here remember Barry crashing the Florida trip.
IMO.