Maybe you are right. I don't think so but obviously there's lots we don't know (including who did or didn't block phone #s. That hasn't been proven yet.)
Personally I think it's very possible the "burn after you read" was an inside joke or was just a lighthearted way to indicate it was a private letter. (And being lightheaded was fine. We have no idea when the letter was written.) The phrase may have related to that movie, or may not have. It's not an original phrase/idea, after all. While it's not the sort of thing I'd write, people write and say all kinds of things-- for example, I have heard people say "I'm going to kill you if you don't stop doing X" or "I could tell you but then I'd have to kill you" and I certainly didn't think any of the speakers intended to kill anyone.
I can't imagine anyone would put in writing anything so sensitive the writer would feel it necessary to request the document be burned after reading. And if the writer thought it was sensitive material, would that request be enough to make the writer feel comfortable? Especially since there are other ways to communicate these days besides letters. It's not the 1500s. (And at any rate, it wasn't burned suggesting to me it was a joke.)
I can think of plenty of reasons a mother might offer assistance and/or advice to her 23-year old son. And until this case came along, I'd never have thought the advice related to a murder. Help breaking away from a toxic relationship? Yeah, I can imagine offering advice on that. And in this case, GP lived in the L's house with BL. How could BL break up with her under those circumstances? He couldn't just tell her to leave even if he wanted to. Or if the letter was written after Moab, there would have been difficulties with BL leaving GP alone out west in a van she
reportedly felt uncomfortable driving. (Although I personally think it's more likely the letter was from earlier as SB said.) And while I don't agree that BL was a "mama's boy" I do think both he and GP were "young for their chronological ages." The court filing from the P's said GP called her parents "almost daily" during the trip. So I do think both GP and BL probably got parental assistance and advice more often than many 20-somethings do.
So far as the cake and saw go, it's not clear to me if the letter said that or if that was an hypothetical example offered by PR (who declined to give specifics since he didn't have a copy of the letter.) From
Patrick Riley, the lawyer for Gabby Petito's parents says that Brian Laundrie's mother wrote a letter to her son offering to help him after he strangled his girlfriend during a VanLife tour of the U.S.
www.dailymail.co.uk
"Riley declined to fully describe the correspondence, saying that he did not want to misquote it."
"He said that though he has read the letter, he does not have a copy of it, but has requested it for the purposes of the lawsuit."
"There was also something referenced in that letter about Gabby and I'd rather not go into it any further at this point. The letter will speak for itself.'
"It was not an offer by the mom to help Brian commit suicide, the lawyer clarified."
'It was an offer that had to do with Gabby,' he said."
At any rate, does anyone really think RL thought she could walk into a jail with a cake? (With or without a saw in it.) And that if she could, and BL was in jail and got a saw that way, he could saw his way through the jail bars and escape? It seems extremely unlikely in the 21th century an educated American businesswoman in her 50s would think that.
JMO