In an amendment to their lawsuit filed earlier this spring, Gabby Petito's parents allege during the search for the young woman, Brian Laundrie's parents knew their son had killed her and knew "the whereabouts of her body."
The amended suit, filed by Petito's parents, alleges the Laundrie family went on vacation to Fort De Soto Park in Florida, while Petito's family was "extremely distraught" and attempting to locate her.
CNN has previously reported that documents from Pinellas County, Florida, showed Laundrie's mother had made a camping reservation at Fort De Soto Park for the first weekend of September, only to change it to a later date and add another person.
Records from the county show the new reservation was made by Roberta Laundrie on September 3, two days after her son returned home. The changed reservation was set to begin on September 6 for three people at Fort De Soto Park, about 75 miles from the family's home.
The lawsuit alleges the Laundrie family went on vacation "knowing that Brian Laundrie had murdered Gabrielle Petito, it is believed that they knew where her body was located, and further knew that Gabrielle Petito's parents were attempting to locate her."
The Laundrie family attorney told CNN they are confident the case will be dismissed, adding in a statement, "The allegations in the amended complaint may now conform to proper pleadings but they do not give rise to liability under the law. Thus, we are still confident the Court will dismiss the action," Steven Bertolino said.
Petito's remains were found in Teton County, Wyoming, in September, a little more than a week after her family reported her missing. The 22-year-old woman died by strangulation, a coroner ruled. She had been on a cross-country trip with Laundrie, who was her fiance. Laundrie returned to the couple's home on September 1 by himself, and left again roughly two weeks later and disappeared.
Laundrie's remains were later found in a Florida reserve and a medical examiner ruled he died by suicide. Nearby, authorities found a notebook in which they said Laundrie claimed responsibility for Petito's death.
The suit accuses Laundrie's parents of acting in an "extreme and outrageous way" for several reasons, including for failing to inform Petito's parents that she was dead and where her remains were located and taking a vacation with their son while the Petito family searched for the young woman.
There is no specific monetary amount listed on the lawsuit, but Petito's parents are asking for damages that exceed $30,000.