MIAMI, UNITED STATES — The boyfriend of Gabby Petito, a social media influencer whose disappearance and death gripped America last year, confessed to her killing in writing before taking his life, the FBI said Friday.

Brian Laundrie killed himself with a bullet to the head amid suspicion about his possible role in the young woman’s death as the two of them took a cross-country road trip, filming themselves along the way and posting the videos online.

His body was found October 20 in a nature reserve in Florida along with some belongings, including a notebook.

“A review of the notebook revealed written statements by Mr. Laundrie claiming responsibility for Ms. Petito’s death,” the FBI said in a statement.

The FBI probe did not identify anyone else involved in the death of Petito, it said.

The 23-year-old Laundrie had disappeared in September, shortly after police described him as a “person of interest” in the investigation into Petito’s death.

Petito’s family, after talking to the FBI, said they were convinced Laundrie killed their 22-year-old daughter.

“The quality and quantity of the facts and information collected by the FBI leave no doubt that Brian Laundrie murdered Gabby,” the family said in a statement released by their lawyers.

The Petito case caused a huge media stir in the United States for weeks. Petito and Laundrie had left New York in July to tour the western United States in a van for four months after Petito quit her job.

For days, they published images on social networks in which they were seen smiling on what appeared to be an idyllic road trip.

But on September 1, Laundrie returned without his girlfriend to North Port, Florida, where they both lived with his family.

His attitude raised suspicions about his role in her disappearance, especially after he refused to answer police questions and then fled on September 13.

Petito’s body was found on September 19 in Wyoming’s Grand Teton National Park, and on October 12 police announced she had been strangled to death.

A video released in September by police in Moab, a small town in Utah, further raised suspicions around Laundrie. In the images, Petito could be seen crying in a car after police intervened in a dispute she had with him.

Petito’s story is all too common in a country where hundreds of thousands of people go missing every year.

But the non-stop media attention devoted to the case sparked controversy over the disproportionate attention paid to the disappearances of white women compared to those from minority groups.