The Petito family lawyer has made a damning claim about what Brain Laundrie did with Gabby Petito's possessions as he travelled back to his home in Florida.
During an interview with Dr Phil, Richard Stafford said Laundrie took Gabby Petito's debit card and spent $1000 to return to Florida without her on September 1.
The FBI has already issued a warrant for Brian's arrest for illegally using a card and pin that did not belong to him on August 30 but did not reveal who the card belonged to.
"I'm sure the FBI has a lot more evidence than we have. You could look at his state of mind by his actions," Mr Stafford said during the interview, which also included Ms Petito's mother Nichole Schmidt and stepfather Jim.
The arrest warrant was issued on September 24 by the US District Court of Wyoming, was for the "use of unauthorised devices."
Court documents revealed the charge against Laundrie was for "knowingly" using a Capital One debit card for at least $1000, "with intent to defraud".
The transactions reportedly took place on August 30 and September 1.
"He ran. He stole her credit [debit per warrant] card. He used her credit card to get home and then ran from the police. That's going to show what he was thinking."
Gabby Petito's father, Joseph, has labelled the Laundrie family "cowards" during the exclusive interview, saying he believes 23-year-old Brian is still alive.
Joe Petito launched the scathing attack against the Laundries during the pre-taped interview which aired overnight in the US, saying he believed Brian was "too cowardly to kill himself".
Mr Petito then raged against Brian's parents, Chris and Roberta Laundrie, who are holed up in their North Port, Florida, home as daily protests against their behaviour carry on outside.
"Anyone who lived in that house is a coward, Mr Petito said. "They don't know how to stand up for their actions".
Mr Petito and his ex-wife, Nichole Schmidt, said they had tried calling and texting the Laundries multiple times, asking for their daughter's whereabouts when she was still missing to no avail.
"It's infuriating," Mrs Schmidt said. "We actually thought that they were both missing at that time."
In one of the text messages, Mr Petito said. "I'm going to call the police, just letting you know, because we have no idea."
"A normal parent when you text someone that [you] are going to call the cops because you can't find your child, they would reply. No response. Nothing."
Mrs Schmidt reported Ms Petito missing on September 11, 13 days after she last heard from her daughter, who was travelling in a white van with Laundrie who returned to Florida with the van on September 1.
Mrs Schmidt, added it was possible Brian was living off the land because "I believe he bragged about that stuff, that he was good at that stuff."
Gabby Petito's stepfather, James Schmidt, also revealed that he was the one to identify her body, which was found in the Grand Teton National Park, in Wyoming, last month.
Mr Schmidt said that when the body was found on September 19, police showed him an article of clothing that he matched as one of her favourite jumpers.
"We knew it was hers," Mr Schmidt said.
"As a mum, I knew she was gone," Mrs Schmidt said.
Mr Schmidt said he had one message for Brian Laundrie – "turn yourself in."
"You're only making it worse. For us and for himself. Let us have some closure," he said.
FBI Denver has said they believe Gabby was killed between August 27 and August 30.
She was last seen on August 27 when Brian reportedly had an argument with a waitress.