According to police, the message read: "Can you help Stan, I just keep getting his voicemails and missed calls"

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Prior to her disappearance, 22-year-old Gabby Petito sent a final text message to her parents that left them worried for her safety.

In the recently unsealed search warrant filed on Sept. 17 for an external hard drive in the van Petito was traveling in, police wrote that her mother, Nicole Schmidt, received an "odd text" from her daughter's phone on August 27.

According to police, the message read: "Can you help Stan, I just keep getting his voicemails and missed calls."

Schmidt told investigators that Stan is Petito's grandfather, but that she doesn't usually refer to him by his first name, the warrant, which was obtained by PEOPLE, states.

"The mother was concerned that something was wrong with her daughter," police wrote.

Gabby Petito and Brian Laundrie
Brian Laundrie, Gabby Petito
| Credit: North Port Police Department/Facebook

This is the last communication that Petito had with her family. After August 27, her phone wasn't operational, and she did not post anything on social media, authorities said in the search warrant.

"Per her family, this was not normal behavior for [Petito], and they became more worried about her," the search warrant reads.

Petito was first reported missing on Sept. 11 after she last had verbal contact with her mother on Aug. 25. On Sunday, the FBI confirmed they discovered a body in Wyoming matching Petito's description.

She had been traveling across the United States in a converted white Ford van with her fiancé, Brian Laundrie. Prior to their cross-country excursion, the couple lived with his parents in Florida.

Gabby Petito
Gabby Petito, Brian Laundrie
| Credit: Gabby Petito Instagram

Laundrie, 23, was identified as a person of interest in the case and refused to sit down with investigators to discuss Petito's whereabouts. He has also since gone missing, with authorities in Florida currently conducting searches for him.

He has not been named a suspect at this time. Laundrie's lawyer has not responded to PEOPLE's requests for comment.

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On Sept. 15, PEOPLE spoke with Petito's father, Joseph Petito, who said his daughter was "amazing."

"She's so artistic. She's an amazing artist. She loves to draw," he said. "She has a great eye with decorating ... She's that flower child type of personality. The old soul, you know?"

"If Woodstock was still going on, she'd still be there, man," Joseph added. "She's a hippie from the '60s, all right? She's a Beatles fan, round glasses ... a free spirit."