Gabby Petito's mother says she thinks Brian Laundrie's family knows about her daughter's killing

• Gabby Petito's mother thinks Brian Laundrie's parents know something about her daughter's disappearance.
• "I would love to just face to face ask why are you doing this, just tell me the truth," she told "60 Minutes Australia."

Gabby Petito's mother said she thinks Brian Laundrie's family "knows most of the information" about her daughter's disappearance and death.

Nicole Schmidt told "60 Minutes Australia" said the family's "silence speaks volumes" after Petito was found strangled to death in Wyoming and Laundrie went missing last month.

"I believe they know probably, if not everything, they know most of the information," she added. "I would love to just face to face ask why are you doing this, just tell me the truth."

Petito and Laundrie - who were engaged - embarked on a cross-country road trip in July and were documenting all of their stops online. In the interview, Petito's mother recalled getting calls, texts, and FaceTime calls every day from the road.

On September 1, Laundrie returned home to North Port, Florida - but without Petito.

Her parents reported her missing on September 11.

Laundrie was then reported missing on September 17, when his parents claimed after he went out for a hike in the Carlton Reserve in Florida, later changing the date that they claimed they last saw him.

Petito's body was found in Wyoming on September 21 in Grand Teton National Park. Her death was ruled a homicide.

Petito's stepfather, Joe Schmidt, said he didn't understand why the Laundries didn't contact them when something appeared wrong.

"Can I make sense of it? No," he said.

"If Brian was staying at my house and Gabby returned to my house without him in his vehicle I'd be on the phone with his parents saying 'we've got an issue. We've got some stuff we gotta talk about, like, now. Call me back,'" he continued.

"It's torturous, if they're withholding something, and they don't want to let us know. Yeah, that's cruel," he added.

Laundrie remains the only person of interest in the case of Petito's death and a manhunt to find him remains active.