FBI confirmed the new details at a briefing in Florida on Wednesday.
"Earlier today, investigators found what appeared to be human remains as well as personal items, such as a backpack and notebook belonging to Brian Laundrie. These items were found in an area that up until recently had been under water," FBI Special Agent in Charge, Michael McPherson said.
WATCH | Brian Laundrie search: FBI holds presser
He says crews will be onsite for several days. There is no information yet on whether those remains are in fact Laundrie's.
In an exclusive interview with Eyewitness News, the family's attorney, Steven Bertolino, says the Laundries are "grieving."
"As you can imagine, the parents are very distraught. Like everyone else they are going to await the results of the forensic investigation before making any further comments. But at this moment in time they're grieving," he says.
The Medical Examiner's Office in Sarasota were called to the preserve where the search for Laundrie was underway, a spokeswoman for the office previously told ABC News.
Laundrie's parents along with the FBI and local authorities found some items possibly belonging to Brian off a trail that he frequented.
The FBI said they were processing the scene after finding "items of interest" at the Carlton Reserve.
Bertolino, released a statement on Wednesday saying, "Chris and Roberta Laundrie went to the Myakkahatchee Creek Environmental Park this morning to search for Brian. The FBI and NPPD were informed last night of Brian's parents' intentions and they met Chris and Roberta there this morning. After a brief search off a trail that Brian frequented some articles belonging to Brian were found. As of now law enforcement is conducting a more thorough investigation of that area."
WATCH | Why former NYPD chief believes latest Brian Laundrie discovery is 'quite strange'
An FBI Evidence Response team is processing the scene and the reserve is closed to the public.
The Pasco County Sheriff's Office confirmed to ABC News that a human remains detection team was requested by North Port Police to go to Myakkahatchee Creek Environmental Park Wednesday to assist in the search for Laundrie. The team consists of one dog, a handler, and two spotters.
WATCH | Special Report: Brian Laundrie search: Possible remains found
One week ago, authorities confirmed that his fiancée Gabby Petito died by strangulation.
Teton County Coroner Dr. Brent Blue had previously ruled Petito's death a homicide, and though the cause was revealed last Tuesday, he declined to provide details about Petito's autopsy or a potential suspect, saying he was limited in what information he could legally release.
Who killed Petito, when she was killed, and what happened leading up to her death remain a mystery.
RELATED | Gabby Petito timeline: Everything we know about her disappearance
Laundrie and Petito had been traveling across the country since June, documenting the trip on social media. They got into a physical altercation Aug. 12 in Moab, Utah, that led to a police stop, which ended with police deciding to separate the quarreling couple for the night. No charges were filed, and no serious injuries were reported.
Even though there are more than 90,000 active missing person cases in the U.S., few met with as much urgency and national attention as that of Petito, who was reported missing in September 11 and whose remains were found more than a week later in Wyoming's Bridger-Teton National Forest.
The 23-year-old Laundrie returned to his home on Sept. 1 without Petito but driving her 2012 Ford Transit. Laundrie had refused to speak to the police and has not been seen since Tuesday, Sept. 14, according to law enforcement officials.
Federal officials in Wyoming last month charged Laundrie with unauthorized use of a debit card, alleging he used a Capital One Bank card and someone's personal identification number to make unauthorized withdrawals or charges worth more than $1,000 during the period in which Petito went missing. They did not say to whom the card belonged.
WATCH: Tracking the Gabby Petito disappearance
The video above is a part of TRACKING, a digital video series from ABC News that uses social media, public records, mapping and expert analysis to piece together timelines of how major news events transpired. Watch more ABC News originals here.
* Get Eyewitness News Delivered
* Follow us on YouTube
* More local news
* Send us a news tip
* Download the abc7NY app for breaking news alerts Submit a News Tip