Cassie Laundrie, the sister of missing Brian Laundrie, has urged her brother to “come forward” amid the nationwide search for him.

Brian Laundrie is at the center of a nationwide manhunt after the body of his girlfriend, Gabby Petito, was found outside a national park in Wyoming back in September. Petito and Laundrie had been on a cross-country road trip before Laundrie returned home to North Port, Florida, without Petito.

Cassie Laundrie told ABC News that she has a simple message for her brother.

“I would tell my brother to just come forward and get us out of this horrible mess,” Cassie Laundrie said in an interview that will air on “Good Morning America.”

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Cassie Laundrie said in the interview that her brother and parents visited her on Sept. 1 — the day Laundrie returned. But she told “Good Morning America” earlier in September that she had not spoken to her brother since he came back to Florida

Now, Cassie Laundrie said she wished her brother had spoken to her sooner.

“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.”

It wasn’t until 10 days later on Sept. 11 that Petito’s family reported Petito missing, which led to a search for her in Wyoming — her last known location. On Sept. 14, Laundrie left his home for a hike. Then, on Sept. 17, Laundrie’s parents told police that Brian had not been seen for days and was missing. Police have been searching for Laundrie since then.

The case took a dark turn on Sunday, Sept. 19, when authorities discovered human remains that matched the description of Petito. Two days later, a Wyoming coroner confirmed the remains were Petito’s and that she had died by homicide, as I wrote for the Deseret News.

The U.S. District Court of Wyoming then issued a federal arrest warrant for Brian Laundrie, saying that had used an “unauthorized access device” related to activities after Petito’s death.

Laundrie’s whereabouts remain unknown.