Gabby Petito's parents are continuing to ask a Florida judge to order Brian Laundrie's mother to turn over an undated letter she wrote to her son that was in his backpack when his body was found, alleging it references "baking a cake with a shiv in it should Brian Laundrie go to prison."

"The letter in question written by Roberta Laundrie references bringing a shovel to help bury a body, and baking a cake with a shiv in it should Brian Laundrie go to prison," the Petitos state in their court response to the Laundries' motion for a protective order.

"A reasonable inference is that the letter was written at a time when Gabrielle Petito was as yet unburied, and Brian Laundrie could go to jail for the crime of murder."

The Petitos argue in the filing that if the jury finds that the letter was written after Gabby's murder, it would serve as evidence that the Laundries knew she was dead.

Roberta and Christopher Laundrie have asked the court for a protective order so they don't have to turn over the letter. Their attorney has alleged the letter was written before Gabby went missing and is not relevant because it was based on repairing Roberta and Brian's mother-son relationship, CNN previously reported.

The Petitos filed a civil lawsuit against the Laundries for emotional distress in connection with Gabby's death while traveling with Brian, her fiancé. Gabby's disappearance in 2021 sparked a nationwide search after Brian returned to their Florida home without her.

Brian was found dead of a self-inflicted gunshot wound around a month after Gabby's remains were discovered in September 2021. Brian admitted that he was responsible for Gabby's death in a notebook found with his remains, according to the FBI.

CNN previously reported on other alleged contents of the letter, including references to "helping (Brian) get out of prison, getting a shovel and some other things," according to Petito family attorney Patrick Reilly. Reilly said he viewed the letter at an FBI regional office. The envelope containing the letter said "burn after reading" according to Reilly.

The Petitos' lawsuit, filed in March 2022, alleges outrageous behavior of intentional infliction of emotional distress by the Laundries during the time Gabby was missing. The Laundries refused to return calls or texts to the Petito family as they were frantically trying to find their daughter, who was missing for weeks before her remains were found, according to the lawsuit.

The Laundries have responded in court filings, arguing they had no duty to Gabby's family.

The next hearing on the case is set for May 24. The case is currently scheduled for trial in 2024.