Theory

Just watched the documentary and the fact Gabby reached out to her ex bf (who eerily looks very similar to Brian with the beard) during the last days of when she was alive, offers a motive for Brian. Perhaps he found out Gabby was Snapchatting & calling her ex and his ego couldn’t handle it. The fact there’s a missed call from her on the day she disappeared could be 1.Brian calling from her phone to confront Jackson about the talk they had 2. Gabby calling while Brian listens to hear the nature of the convo 3. Her calling on her own as a way of reaching for help. Unfortunate that this call was never connected to find out for sure.

Just seems to be the simplest explanation. Brian finds out his gf is talking to her ex during their coupley van life trip, confronts her about it. Argument ensues, and we all know what happened.

P.S- the Laundrie family are the absolute worst