I was speaking to the story from Reilly reported in the earlier link-- that the letter was found in the van but moved to the house. If that story had been true, what evidence do we have the FBI kept a copy of the letter after leaving the original with the Laundries
after removing it from the van in early Sept? Why would the FBI have done that? Either it was potential evidence in which case the FBI would not have left the original with the L's OR it wasn't potential evidence in which case the FBI would not have made a copy.
Reilly's story
has changed over time. Here's a slightly different account from him for how the letter was found during the house search on Sept 20:
Brian Laundrie's mother offered him a shovel in ‘burn after reading’ note
"Reilly, the attorney for the Petito family, said that the FBI found the letter in a box in a closet in the Laundries' house. It contained items from the van he and Petito were traveling in, Reilly added."
So I guess because the letter was in a box with items that seemed to have been in the van, Reilly assumed it had been in the van too? Seems to be an iffy conclusion to me but if that's true, that would, IMO, argue the letter was written earlier, before the trip began, not later after GP was dead.
JMO