'We beg you to tell us': Attorney accuses Laundrie family of withholding Gabby Petito's location

Christopher and Roberta Laundrie, the parents of Brian Laundrie, know the location of Gabrielle Petito, who went missing while on a cross-country trip with Brian – according to Petito's parents and step-parents.

Nicole and Jim Schmidt, Gabby's mother and stepfather, and Joe and Tara Petito, Gabby's father and stepmother, penned a letter to the Laundries, pleading for information on their daughter's whereabouts.

According to multiple sources, including law enforcement and social media, Brian and Gabby were last together in Utah, near Arches National Park. Gabby's family says they last heard from her on August 25. They say a text message was sent from Gabby's phone on August 30; however, they do not believe Gabby sent the message. 

Attorney Rick Stafford, who read a letter from the Schmidt and Petito families during a press conference Thursday, said Brian Laundrie returned to his parents' home in North Port, Florida – driving Gabby's camper van – on September 1.

MORE: Gabby Petito body camera video reveals emotional encounter with boyfriend Brian Laundrie

In the letter, Gabby's family pleads with Brian's parents to tell law enforcement what they know about the last time their son saw their daughter.

"We are writing this letter to ask you to help find our beautiful daughter. We understand you are going through a difficult time and your instinct to protect your son is strong. We ask you to put yourselves in our shoes. We haven't been able to sleep or eat and our lives are falling apart," the letter reads. "We believe you know the location where Brian left Gabby. We beg you to tell us. As a parent, how could you let us go through this pain and not help us? As a parent, how could you put Gabby's younger brothers and sisters through this?"

MORE: Gabby Petito's family, North Port police chief express frustration with Brian Laundrie's silence

The letter continues, pointing out that Gabby and Brian planned to be married and asked the Laundries how they could keep the location of their future daughter-in-law concealed.

"All we want is Gabby to come home. Please help us make that happen," the letter states.

Read the full letter here:

After reading the letter, Stafford said, "every day that this goes on, they get more and more desperate. They're at the point that that desperation is turning to anger. They know that the Laundries know where their daughter is and they will not tell them. That's infuriating."

RELATED: Timeline of Gabby Petito's disappearance, investigation

Earlier Thursday, police in North Port also called on the Laundrie family to come forward with any information that might help them find Gabby.

"We share the frustration with the world," said Chief Todd Garrison during Thursday's press conference. "Two people went on a trip, and one person returned. That person who returned isn’t providing information."

He went on to say that the only information they received from Laundrie's attorney was a statement that "there will be no further statements made."

This story was reported from Tampa, Florida.