Good question. Through my personal experience, there has always been a bit of hindsight being 20/20. IMHO, I don't think that BG necessarily killed before this, but I wouldn't be a bit surprised, when he is finally caught, to discover former partners/spouses/children to come forward and talk of physical and/or mental abuse. I don't honestly believe that Joe Schmo is going to wake up one morning and say, "Man, I've had a rough week. Think I'll go kill someone today!" but I HAVE seen cases where there has been a pile-on effect: years of smaller incidents and grievances culminating in this one episode. If I thought BG resembled someone I knew, I would also ask myself if my suspect had been going through a tough time lately: lost his job, gone through a divorce, had some financial trouble, lawsuit trouble, etc.
I have personally gone back and forth on this case as to BG's previous history in regards to the planning. Either he is VERY cunning and this was well-planned out from the beginning or he is just very, very lucky.