Brian Laundrie's sister, Cassie Laundrie, broke her silence in an exclusive interview with GMA on Thursday.
"Obviously me and my family want Gabby to be found safe," Laundrie said. "She's like a sister and my children love her, and all I want is for her to come home safe and found and this to be just a big misunderstanding."
WATCH | Exclusive interview with Brian Laundrie's sister:
Petito has been missing since late August while on a cross-country trip with Laundrie.
Why isn't Brian Laundrie talking? Legal Analyst Dan Abrams explains
The letter from Petito's family was read by the family's attorney, Richard Stafford, on Long Island, where both Petito and Laundrie are originally from despite having lived in Florida for the past two years with Laundrie's parents.
Click here to read the full letter.
So far, the Laundries have not aided the investigation, citing advice from legal counsel, which authorities say is hindering the investigation.
Brian Laundrie has been named a person of interest in the case, and the letter comes on the same day police in Utah released body camera footage of officers' encounter with the couple on August 12.
WATCH THE FULL BODY CAM VIDEO:
Laundrie drove the Ford Transit van back to Florida on September 1 alone, police said. Petito's family filed a missing persons report last Saturday with Suffolk County police.
Gabby Petito: Timeline of everything we know about her disappearance
Laundrie's attorney, Steven Bertolino, said the Laundrie family is hoping for Petito's safe return, but he's asked them not to speak with investigators.
Petito is described as a white female, approximately 5-foot-5 and 110 pounds.
She has blonde hair, blue eyes, and several tattoos, including one on her finger and one on her forearm that reads "Let it be."
Detectives are asking anyone with information on Petito's disappearance to contact Suffolk County police at 1-800-220-TIPS, the North Port Police Department at 941-429-7382, or the FBI at 1-800-CALL-FBI.