Brian Laundrie used Gabby Petito’s bank card in Wyoming just three days after the slain 22-year-old Long Island native was last seen alive, her family’s lawyer said Tuesday.

Petito was last spotted at a Wyoming restaurant on Aug 27, while Laundrie, 23, returned home alone in her van on Sept. 1 — and the boyfriend has since gone on the run from the feds.

“You can look at his state of mind by his actions,” Petito family attorney Richard Stafford said on the “Dr. Phil” show on CBS-TV.

“He ran, he stole her credit card, he used her credit card to get home, and then ran from the police,” Stafford said. “That’s going to show a lot what he was thinking back then.”

Federal authorities in Wyoming issued an arrest warrant for Laundrie on Sept. 23 for allegedly using a stolen card “on or about August 30, 2021, through and including on or about September 1, 2021” and “obtained things of value aggregating to $1,000 or more.”

But the FBI had not identified the victim of the fraud and had not said it was Petito.

The Blue Point native’s body was found at a campground at the Teton-Bridges National Forest in Wyoming, with her death classified as a homicide.

Laundrie lawyered up and refused to talk to authorities after he returned home without her on Sept. 1 and later disappeared from his parents’ Florida home.

The fugitive’s parents told police he went on a hike on Sept. 14 at the nearby Carlton Reserve and never returned.

On Tuesday, Laundrie family attorney Steven Bertolino said in a statement that “upon further communication with the FBI,” they “now believe” that Laundrie left the house a day earlier, on Sept. 13.

Laundrie is the only person of interest in Petito’s disappearance and death and is now the subject of a massive FBI-led manhunt.

Petito was last seen alive with Laundrie on Aug. 27 at the Merry Piglets restaurant in Jackson Hole, Wyoming, where witnesses said Laundrie flipped out on the staff.