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.
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The FBI's Denver office said in a news release a comparison of dental records confirmed that the remains were Laundrie.
The FBI statement did not list a cause of death. It wasn't clear how long the remains may have been submerged in water.
Laundrie family attorney Steven Bertolino said his parents, Chris and Roberta Laundrie, would have no further comment at this time.
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"His parents are a mess. They are extremely upset. They're 'extremely distraught' is the word I've been using, but I don't think that accurately describes it," said Bertolino.
Eyewitness News reporter Kristin Thorne asked Bertolino if he believes that Brian killed himself.
"We're going to wait till we have more information from the Medical Excaminer's office. I'm told we may have some information (Friday) afternoon," Bertolino added.
The Petito family declined to comment on the development.
"They are grieving the loss of their beautiful daughter. Gabby's family will make a statement at the appropriate time and when they are emotionally ready," their attorney said.
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, Florida.
The investigation into Petito's slaying, however, is not yet concluded. But only Laundrie has ever been identified by law enforcement officials as a person of interest in the case.
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On Thursday morning, several K-9 units and off-road vehicles were observed entering the reserve to further search the area. McPherson says crews will be onsite for several days.
Laundrie's parents, Chris and Roberta Laundrie, helped law enforcement with finding the items, which Bertolino described as happenstance.
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He said Laundrie's parents informed the FBI and the North Port Police Department on Tuesday night that they wanted to visit the park Wednesday morning to search for their son. Law enforcement met them there and closely accompanied them as they entered the park, Bertolino said.
"As they went further in, Chris ventured off the trail into the woods," Bertolino said. "He was zigzagging in different areas. Law enforcement was doing the same thing. And Roberta Laundrie was walking down the trail. At some point, Chris locates what's called a dry bag. The dry bag is a white bag, laying in the woods, say 20 feet or so off the trail."
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The dry bag was in some brambles, Bertolino said, and he didn't want to move it because he wanted his law enforcement to see it. However, Chris Laundrie "couldn't find the law enforcement" because they were out of sight and didn't want to leave the bag there with a news reporter standing nearby, so he picked it up, Bertolino explained.
"He did meet up shortly with law enforcement, they looked at the contents of the bag," he said. "At that time, law enforcement officers showed him a picture on the phone of a backpack that law enforcement had located also nearby and also some distance off the trail....At that point, the Laundries were notified there was also remains near the backpack, and they were asked to leave the preserve."
The remains were found "about 2 to 3 miles inside the Carlton Reserve, or about a 45-minute walk" from the entrance at Myakkahatchee Creek Environmental Park, North Port police spokesperson Josh Taylor said.
When asked why the parents chose to go to the park on Wednesday, Bertolino said it was the first day it was reopened to the public.
"The parents had assumed that the experts, the FBI and all the tracking teams they had would be able to locate Brian based upon the information that we had provided them to the specific areas and trails in the park that Brian liked to visit," Bertolino said. "The park had been closed to the public. There was really no other reason for the Laundries to go search anywhere else.
The discoveries came during an exhaustive search for Laundrie that stretched over a month as authorities tried to piece together what happened to him and Petito during their road trip through the Western US this summer.
The couple first met as teenagers on Long Island, New York, and more recently moved to Florida's Gulf Coast to live with his parents.
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They first gained an online following while on their trip in a converted Ford Transit van in videos filled with happy scenes that may have concealed deeper problems. After Petito disappeared, the case became a true-crime obsession on social media.
The couple was stopped Aug. 12 by police in Moab, Utah, after they had a physical altercation, but no domestic violence charges were filed. The police department there is conducting an internal review to determine if policy was followed.
Laundrie returned home alone Sept. 1 in the van the couple took on their trip, which was later impounded by authorities. He was reported missing after telling his parents that he was going for a hike in the Carlton Reserve.
Her body was found Sept. 19 on the edge of Wyoming's Grand Teton National Park, which the couple had visited.
Teton County Coroner Dr. Brent Blue ruled her death a homicide and said she died by manual strangulation.
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Laundrie had not been charged in her death, although he was indicted for allegedly using two financial accounts that did not belong to him in the days following her killing.
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