By Aya Elamroussi, Taylor Romine, Leyla Santiago, Randi Kaye and Sara Weisfeldt, CNN
(CNN) -- The FBI's Denver office said Thursday that remains found a day earlier in a Florida nature reserve are those of Brian Laundrie, who disappeared last month just days after his fiancée Gabby Petito was reported missing.
The FBI said dental records confirmed the identification.
The identification came hours after police in North Port, Florida, said the remains that were found were skeletal and belonged to a human.
"They are human remains, no doubt there. I would say that the remains were consistent with one individual, you know skeletal remains," North Port police spokesperson Josh Taylor told CNN.
Investigators also found clothing believed to be consistent with what Laundrie was wearing when he took off September 13, according to Taylor.
Less than a week after Laundrie went missing last month, authorities in Wyoming found Petito's remains in a national forest. Her death was ruled a homicide by manual strangulation.
On Wednesday, investigators also found a backpack and a notebook belonging to Laundrie, 23, near the remains while they were searching the Carlton Reserve in North Port, according to FBI Special Agent in Charge Michael McPherson.
"The notebook to my understanding has not been opened. You know, that will need to be processed," Taylor said.
A source with knowledge of the investigation told CNN the notebook is "possibly salvageable." The source said the notebook was "outside of the dry bag."
"It had been clearly wet and they are going to use any potential means to dry that out before opening it," according to the source, who added: "They'll be very careful with it."
The source said it is unclear how the notebook ended up outside the dry bag.
When Taylor was asked about whether a weapon was found, he said he could not comment.
When asked if there is an ongoing search for the murderer of Gabby Petito, he responded, "That is certainly not in the North Port Police Department's purview."
During a search with police, Brian's father, Chris Laundrie, was the first to spot an item belonging to his son, according to Taylor.
Laundrie family attorney Steven Bertolino told CNN's Chris Cuomo on Wednesday that "the probability is strong that it is Brian's remains."
The discovery came on Wednesday morning when Laundrie's parents and law enforcement searched an area of the reserve that had been underwater but recently reopened to the public.
"It's quite sad, you can imagine as a parent, finding your son's belongings alongside some remains. That's got to be heartbreaking. And I can tell you that they are heartbroken," Bertolino told Cuomo.
Search conditions had been very difficult
Lee County Sheriff Carmine Marceno said Thursday law enforcement had been searching in treacherous conditions, including nearly chest-high water full of snakes and alligators.
"These are very, very difficult conditions. You're searching in areas that you just can't walk up and look. It's not like you're searching a house or a car," he said. "These areas are huge and they're covered by water."
The exhaustive search for Laundrie 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.
Petito, 22, disappeared on the trip amid tensions in their relationship, and her remains were later found near where the couple had last been seen together.
Laundrie, who had returned by himself to his parents' home in Florida, refused to talk with investigators and didn't return after telling his parents he was going to the nature reserve to hike.
He was not charged in Petito's death, although he was indicted for allegedly using two financial accounts that did not belong to him in the days following her killing.
Authorities, including several K-9 units and off-road vehicles, returned to the reserve on Thursday morning to further search the area.
Brian Laundrie's parents were on scene when remains were found
Laundrie's family had declined to talk publicly following legal advice, but they had directed authorities to where they believed Laundrie may be staying in the reserve, Bertolino said.
The parents -- Chris and Roberta Laundrie -- joined in the search Wednesday morning and found a bag belonging to their son at the park, which their attorney described as "happenstance."
According to Bertolino, 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. He was zigzagging in different areas, law enforcement was doing the same thing. And Roberta Laundrie was walking down the trail," Bertolino said. "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."
The dry bag was in some brambles and he didn't want to move it because he wanted his law enforcement to see it, Bertolino said. However, Chris Laundrie couldn't find law enforcement 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. 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," Bertolino told CNN.
"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, Taylor said Wednesday.
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."