(CNN) What appears to be human remains and items belonging to Brian Laundrie, including a backpack, have been found in the Carlton Reserve in North Port, Florida, according to FBI Special Agent in Charge Michael McPherson.
Another one of the items found was a notebook belonging to Laundrie, who McPherson said was "a person of interest in the murder of Gabby Petito."
The apparent remains were found in an area that has been under water until recently, he said.
A source close to the investigation told CNN that the apparent human remains "appear to have been there a while."
The source said "based on the condition of the remains, it may take some time to officially identify. It is going to be a very thorough process with the medical examiner."
North Port police spokesperson Josh Taylor said 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.
Family attorney Steve Bertolino told CNN's Chris Cuomo that the Laundrie parents -- making their first visit to the park since its reopening -- helped with the discovery. "As happenstance was, they stumbled upon these items," he said.
The area where the discovery of remains was made was the "very area of the park that we initially informed law enforcement on," Bertolino said, referring to a meeting with law enforcement on September 17.
Laundrie's parents had informed the FBI and the North Port Police Department on Tuesday night that they intended to come to the park on Wednesday morning to search for him, Bertolino said. Law enforcement met them there Wednesday morning, he said.
The parents walked the trail followed closely by law enforcement personnel, "certainly within eye shot," the attorney 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."
Bertolino said, according to Chris Laundrie, the dry bag was in some brambles and he didn't want to pick up the bag, because he wanted his law enforcement to see it. However, Bertolino said Laundrie "couldn't find the law enforcement," because they were then out of sight and didn't want to leave the bag there with a news reporter standing nearby, so he picked it up.
"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."
Bertolino called the suggestion that Chris Laundrie had planted the dry bag "hogwash."
The attorney said the family was heartbroken by the discoveries today.
The FBI Tampa's Evidence Response Team is on the scene using "all available forensic resources" to process the area. According to McPherson, it's likely the team will be on the scene for several days.
"I know you have a lot of questions, but we don't have all the answers yet," he said reading a statement for the media.
The discovery comes 37 days after Laundrie, the fiancé of Petito, was reportedly last seen by his parents.
Earlier, the Sarasota County medical examiner and a cadaver dog were called to the park and aerial footage showed activity in the Carlton Reserve near the Myakkahatchee Creek Environmental Park where Laundrie's car was found parked in September.
The Sarasota County Medical Examiner was called to the scene, and the Pasco County Sheriff's office said a cadaver dog and two spotters were also on site. The Sarasota County Sheriff's Office Emergency Response Team and the Lee County Sheriff's Office were also now on scene along with a mobile unit.
The discovery comes amid an exhaustive search for Laundrie that has now stretched over a month and as authorities try to piece together what happened to Petito.
The Myakkahatchee Creek Environmental Park is on 160 acres of heavily wooded land in North Port, with trails and a camping area. The park connects to the Carlton Reserve, a 25,000-acre nature reserve that has been the primary search location for investigators.
Searchers had previously used swamp buggies, divers and airboats to scour the swampy terrain, but the area has dried out recently due to clearer weather.
Petito, 22, and Laundrie, 23, traveled around the western US in a white van this summer, all while regularly posting photos and stories to their social media pages. Those posts abruptly stopped in late August, though, and Laundrie then returned by himself to their home in North Port, where they lived with his parents, on September 1.
Petito's family, unable to get in contact with her, reported her missing 10 days later, launching a national search. Laundrie declined to cooperate with the investigation into her whereabouts, and soon after, he also went missing. His family told investigators they believed he had gone to a sprawling nature reserve nearby.
Petito's remains were found in a national forest in Wyoming on September 19 near where the couple had last been seen together. Teton County Coroner Dr. Brent Blue ruled her death a homicide and said that she died by manual strangulation.
"We believe this was strangling by a human being," Blue told CNN's Anderson Cooper.