Petito's body was found in Wyoming in September, and Laundrie's body was found in a Florida reserve weeks later.
The FBI in Denver, which led the investigation, said a notebook, a backpack and a revolver were found near the remains later identified as Laundrie. In the notebook was Laundrie's written confession, the FBI said
"A review of the notebook revealed written statements by Mr. Laundrie claiming responsibility for Ms. Petito's death," the FBI wrote.
The FBI on Friday also confirmed that Laundrie had been "attempting to deceive law enforcement by giving the impression that Ms. Petito was still alive" by continuing a text chain between their two phones after she is believed to have died. Laundrie used Petito's debit card while driving alone from Wyoming to his parents home in Florida in early September, the FBI said.
Petito, 22, had been on a cross-country trip with her fiancé. Her family reported her missing on September 11. Her body was found in the Spread Creek Dispersed Camping Area — where she and Laundrie had previously been seen together — seven days later.
Laundrie became the focus of the investigation, but he disappeared from his parents Florida home while authorities were still searching for Petito. His remains were eventually found after a a weeks-long manhunt at the Carlton Reserve, and authorities determined he died of a self-inflicted gunshot wound.
Petito died of "blunt-force injuries to the head and neck, with manual strangulation," the FBI said on Friday. The Teton County Coroner's office had previously announced in October that she died of strangulation.
"The investigation did not identify any other individuals other than Brian Laundrie directly involved in the tragic death of Gabby Petito," the FBI concluded.