Long Island native Gabby Petito and her boyfriend Brian Laundrie went on a cross-country trip in July, but only Laundrie returned home -- he drove back to Florida in Petito's white Ford Transit van.Petito's body was found in Wyoming's Grand Teton National Park, but Laundrie vanished last Tuesday and authorities have had no success in locating him, despite help from body hunters and volunteers.According to one expert, law enforcement agencies should focus on Brian's parents, Christopher and Roberta, if they want to find him.Read more below.Laundrie 'Could Be Anywhere'Former United States Marshal Lenny DePaul believes Laundrie "could be anywhere" at this point, but he's bound to "mess up.""It doesn’t matter. Mexico. He can be on a boat sitting off the coast of Cuba. It doesn’t matter. He’s gonna mess up. He’s going to make the mistake," DePaul told The New York Post."I would run as fast and as far as I could, too, if I were him. Any way you look at it, it’s not good for him," the 30-year veteran of the Marshal Service added.Parents Are KeyDePaul said that the investigators have to "tear" Laundrie's world "upside down" and focus on his parents."If I was sitting down with his mother and father at the kitchen table the first question I would ask them, 'If you knew where your son was would you tell me?'" DePaul noted."And nine times out of 10 they’re going to tell you, 'No I would not.' Now that tells me two things. Number one they know where he is. And number two I’m going to take a hard look at mom and dad."Federal WarrantLast week, the FBI obtained a federal warrant for Laundrie in Wyoming because he allegedly made purchases with somebody else's credit card.According to DePaul, law enforcement can use this warrant as "leverage" against Laundrie's family and friends because eventually Laundrie will reach out to somebody he knows.DePaul stressed that investigators are most likely already questioning Laundrie's friends anyway."Our technical operations groups, our electronic surveillance units, our financial surveillance units, these guys are all over this thing like a cheap suit," he said.FBI Visited Laundrie Family HomeOn Thursday, the FBI paid another visit to the Laundrie family's home in North Port, Florida.Two agents arrived to the home in a black SUV. They brought a large paper bag inside, and one agent climbed into a camper van parked outside the house, as reported by CNN.According to Laundrie family's lawyer Steven Bertolino, the FBI was there to collect Laundrie's personal items."The FBI is at the Laundrie home today to collect some personal items belonging to Brian that will assist the canines in their search for Brian. There is nothing more to this," Bertolino said.