gabby petito
Laundrie, the only person of interest in his girlfriend Gabby Petito's death, remains wanted for bank fraud.
The 22-year-old's remains were found in Wyoming late last month.
"Come forward," Cassie Laundrie urged her brother, the subject of a US search since the discovery of fiancée Gabby Petito's body.
The disappearance of the van-life blogger became an overnight internet obsession.
The 22-year-old lifestyle blogger's death has been determined to be homicide.
The message left her mother concerned, the newly released documents state.
Remains matching Petito's description were found in Wyoming, US, on Sunday.
The 22-year-old was last seen in Grand Teton National Park. The FBI announced the tragic discovery during a press conference on Sunday.
The 22-year-old influencer went missing on a road trip with her boyfriend, who now refuses to speak with the police.