It was the first time authorities squarely pinned the blame for Petito's death on Laundrie, though he was the prime suspect all along.
Investigators meanwhile announced that Laundrie, 23, had sent text messages to intentionally deceive people that Petito, 22, was still alive after he beat and strangled her in late August, according to a statement released by the FBI in Denver.
The FBI says their "investigation did not identify any other individuals other than Brian Laundrie directly involved in the tragic death of Gabby Petito."
When Laundrie's body was found, a backpack with a notebook was found nearby.
The FBI wrote, "a review of the notebook revealed written statements by Mr. Laundrie claiming responsibility for Ms. Petito's death."
Laundrie died from a self-inflicted gunshot wound some time later in a Florida nature reserve.
The FBI did not specify what, exactly, Laundrie had written in the notebook and in the texts he'd sent to mislead. The texts were sent between Laundrie's phone and Petito's phone, according to the statement.
Petito's remains were found in Wyoming on Sept. 19, one month after she disappeared while on a road trip with Laundrie. A coroner determined she'd died about three weeks earlier of "blunt-force injuries to the head and neck, with manual strangulation."
An attorney for Laundrie's family released the following statement:
"Gabby and Brian are no longer with their families and this tragedy has caused enormous emotional pain and suffering to all who loved either or both of them. We can only hope that with today's closure of the case each family can begin to heal and move forward and find peace in and with the memories of their children."
The couple documented their trip on Instagram. They crossed Colorado and on Aug. 12 were stopped by police in Moab, Utah, after the two got into a scuffle.
Police video showed Petito describing a fight that escalated. Police concluded Petito was the aggressor but officers decided to separate them for the night rather than file charges.
Petito's family met with the FBI on Thursday and the investigation will be closed in the near future.
RELATED | Investigation completed in Gabby Petito, Brian Laundrie August domestic incident in Utah
(The Associated Press contributed to this report.)
* More Long Island news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube
Submit a News Tip