Cassie Laundrie said she has a message for her missing brother, who has been the center of a nationwide manhunt after the body of his girlfriend, Gabrielle "Gabby" Petito, was found in Wyoming last month.

       "I would tell my brother to just come forward and get us out of this horrible mess," Cassie Laundrie told ABC News in an interview airing Tuesday on "Good Morning America."

       Brian Laundrie, 23, and Petito, 22, were traveling across the country this summer in Petito's white 2012 Ford Transit and were documenting their road trip on social media. On Sept. 1, Brian Laundrie returned to his parent's home in North Port, Florida, by himself in Petito's van, according to authorities. Petito was reported missing on Sept. 11 by her family in Long Island, New York, authorities said.

       MORE: Gabby Petito case: Timeline of travel blogger's disappearance

       Cassie Laundrie, who lives in Florida with her husband and two sons, told ABC News that her brother and parents stopped by for a visit the day he returned.

       "I really wish he had come to me first that day with the van," she said, "because I don't think we'd be here."

       North Port Police Department/Handout via Reuters, File

       Gabrielle "Gabby" Petito, 22, poses for a photo with her boyfriend, Brian Laundrie, in this undated handout photo. Petito's body was discovered in the Bridger-Teton National Park in Wyoming in September 2021, after she traveled across the country with Laundrie in a van and never returned home.

       Brian Laundrie was subsequently named a "person of interest" in Petito's disappearance. He has refused to speak to investigators and has not been seen since Sept. 14, authorities said.

       On Sept. 19, the Teton County Coroner's Office in Wyoming announced that a body was recovered in the Bridger-Teton National Park. Two days later, the coroner confirmed the remains were that of Petito and that an initial determination showed she had died as a result of homicide. A federal arrest warrant was later issued for Brian Laundrie in Wyoming, pursuant to a federal grand jury indictment related to his "activities" following Petito's death, according to the Federal Bureau of Investigation.

       MORE: Police called to Laundrie home day before Petito reported missing: Live updates

       The twist and turns of the case have grabbed national attention, as the search for Brian Laundrie continues.

       Cassie Laundrie told ABC News that she becomes worried when she thinks about her brother and where he might be.

       "I hope he's OK," she said, "and then I'm angry and I don't know what to think."