1:24 PM PT -- Laundrie family attorney, Steven Bertolino, tells TMZ, "As I have maintained over the last several months, the Laundrie‘s have not publicly commented at my direction which is their right under the law. Assuming everything the Petitos allege in their lawsuit is true, which we deny, this lawsuit does not change the fact that the Laundries had no obligation to speak to Law Enforcement or any third-party including the Petito family. This fundamental legal principle renders the Petito’s claims to be baseless under the law."
The parents of Gabby Petito want justice for their daughter -- suing the parents of her killer, Brian Laundrie -- for allegedly knowing more about Gabby's death than they let on.
According to the lawsuit, obtained by TMZ, Gabby's parents say Chris and Roberta Laundrie knew their son had murdered Gabby and believed they were in the process of helping him leave the country.
The docs also mention Gabby's autopsy revealed she'd suffered blunt force injuries to both her head and neck ... additional details from the fact she had been strangled to death.
The lawsuit, filed by Gabby's dad, Joseph Petito, and mom, Nichole Schmidt claim after her death, Brian used Gabby's phone to send text messages ... making it seem like she was still alive.
Gabby's parents say in one of the texts allegedly sent to Schmidt by Laundrie from Gabby's phone, he referred to Gabby's grandfather by his real name, Stan, something she would never have done.
The lawsuit claims Brian was using Gabby's phone up until at least August 30 -- 3 days after she was murdered -- to communicate with Schmidt, saying there was poor cell service in Yosemite.
What's more ... Gabby's parents say they believe it was on August 28, a day after her murder, when Brian told his parents what had happened. The lawsuit alleges it was that same day when the Laundries contacted an attorney ... and hired him a few days later.
Gabby's parents say prior to her disappearance, they had a pleasant relationship with the Laundries, but as the situation got worse, Brian's mom allegedly blocked Gabby's mom's cellphone as well as her account on Facebook.
While the docs don't get into detail on exactly how ... they read, " ... Christopher Laundrie and Roberta Laundrie were keeping the whereabouts of Brian Laundrie secret, and it is believed were making arrangements for him to leave the country."
Gabby's parents say they suffered emotional distress, and are asking for an unspecified amount in damages.
Originally Published -- 11:46 AM PT