NORTH PORT, Fla. (NewsNation Now) — The Laundrie family attorney Tuesday said Brian Laundrie’s parents now believe they last saw him Sept. 13, a day earlier than they’d previously told investigators.

“The Laundries were basing the date Brian left on their recollection of certain events,” their lawyer, Steven Bertolino, told NewsNation. “Upon further communication with the FBI and confirmation of the Mustang being at the Laundrie residence on Wednesday Sept. 15, we now believe the day Brian left to hike in the preserve was Monday Sept. 13.“

Bertolino also explained why Brian Laundrie left his girlfriend Gabby Petito in the middle of a cross-country road trip, just weeks before her body was discovered at a camping area in the Bridger-Teton National Forest in Wyoming.

“Brian flew home to Tampa from SLC on 08/17 and returned to SLC on 08/23 to rejoin Gabby,” Bertolino said in a series of texts to NewsNation. “To my knowledge Brian and Gabby paid for the flights as they were sharing expenses.  Brian flew home to obtain some items and empty and close the storage unit to save money as they contemplated extending the road trip.”

Bertolino’s texts came as Brian Laundrie’s sister, Cassie Laundrie, took questions from a small group of protesters outside her home Monday and clarified questions around the timing of her brother’s disappearance.

She confirmed that Brian Laundrie flew home to Florida from the Western U.S. on Aug. 17, five days after he and Gabby Petito were pulled over and separated by police in Moab, Utah.

The group asked whether Cassie Laundrie believed her brother killed Gabby Petito, and whether she thought he was still alive. Her answers to both questions were the same: “I don’t know.”

Watch Cassie Laundrie’s interview here.

The FBI has issued an arrest warrant for Brian Laundrie. He is wanted for “use of unauthorized access device” related to his activities following Petito’s death. The FBI says he used a debit card and a PIN to access two bank accounts Aug. 30 and Sept. 1. He is also the sole person of interest in Petito’s murder.

Brian Laundrie’s parents now say they last saw him Sept. 13 as he headed for a hike at the Carlton Reserve in Florida, though they did not report him missing until a few days later. Investigators have focused an intensive search on the area. 

Petito vanished while on a cross-country road trip with Brian Laundrie in a converted camper van. The trip was well documented on social media until it abruptly ceased, allegedly somewhere in Wyoming. Petito, 22, was reported missing Sept. 11 by her parents after she did not respond to calls and texts for several days. Her body was discovered days later near Grand Teton National Park.

The Associated Press and NewsNation affiliate WFLA contributed to this report.

This story is developing. Refresh for updates.