(NewsNation) — A notebook reportedly belonging to Brian Laundrie, in which he appears to claim responsibility for killing Gabby Petito in September 2021, was publicly released by the Laundrie family attorney Friday.

But there is at least one other piece of evidence that might come as a surprise to those following the case, according to the attorney for the Petito family.

Patrick Riley appeared on NewsNation this week, claiming the Laundries’ attorney is in possession of a letter from Roberta Laundrie to her son Brian that apparently reads “burn after you read this” on the envelope.

Riley claimed the letter was not within the notebook released on Friday.

“My understanding is, that the letter, at one point, had been in the van. But then it was taken from the Laundrie home during the time when the search warrant was executed,” Riley said.

Riley claims the content of the letter came as a “surprise” to Laundrie family attorney Steven Bertolino.

“He has the original letter,” Riley claims. “And I’ve asked him to maintain that for purposes of the litigation.”

Riley said he couldn’t reveal exactly what was in the letter, other than “an offer from Roberta Laundrie to assist her son.”

“It’s a pretty interesting, pretty odd letter,” Riley said.

The letter itself is not dated, but it appears that the letter was written within the time that Petito was murdered and Brian Laundrie committed suicide, Riley claims.

Riley said the letter also referenced Gabby Petito, but he declined to comment further.