ST. PETERSBURG, Fla. — The FBI on Thursday identified human remains found in a Florida nature preserve as those of Brian Laundrie, a person of interest in the death of girlfriend Gabby Petito while the couple was on a cross-country road trip.

The remains, a backpack and notebook believed to belong to Laundrie were discovered Wednesday in a Florida wilderness park, according to the FBI. The area where they were found had been under water during earlier searches.

The FBI’s Denver office said in a news release that a comparison of dental records confirmed that the remains were Laundrie.

The discovery of the remains concluded a massive search involving federal, state and local law enforcement that began shortly after Laundrie disappeared Sept. 14, two weeks after the 23-year-old returned alone to his parents’ home in North Port, Fla.

The body of Petitio, 22, was found Sept. 19 on the edge of Wyoming’s Grand Teton National Park, which the couple had visited. The coroner there concluded she died of strangulation and her body had been where it was found for three or four weeks.

The couple was stopped Aug. 12 by police in Moab, Utah, after they had a physical altercation, but no charges were filed.