Potential human remains have been found along with items believed to belong to Brian Laundrie, whose girlfriend Gabby Petito was murdered, the FBI has said.
Laundrie, 23, is a person of interest in the killing of Ms Petito, who was reported missing September 11 by her parents while the young couple was on a cross-country trip in the west of the US.
Michael McPherson, chief of the Tampa FBI office, said at a news conference that it will take time to identify the remains, which forensic teams were examining.
He added they were found near a backpack and a notebook linked to Laundrie.
“We are working diligently to get those answers for you,” Mr McPherson said, adding that the items and remains were found in a swampy area – home to alligators, snakes, coyotes and other wildlife – that had previously been underwater.
“It’s likely the team will be on site for several days.”
Laundrie’s parents, Chris and Roberta Laundrie, took part in the search on Wednesday with the FBI and police from North Port, Florida, more than a month after Laundrie was reported missing after heading to the vast Carlton Reserve park.
“After a brief search off a trail that Brian frequented some articles belonging to Brian were found,” Laundrie family lawyer Steven Bertolino said in a text to The Associated Press.
“As of now law enforcement is conducting a more thorough investigation of that area.”
The Sarasota County Medical Examiner’s Office confirmed it had been summoned to the reserve but would not comment further.
Ms Petito’s body was found on September 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.
Laundrie returned home alone on September 1 in the Ford van the couple took on their trip.
He was reported missing after telling his parents on September 14 that he was going for a hike in the Carlton Reserve, a nature preserve in Sarasota County that has for weeks been a key area in the search.
The activity on Wednesday was focused on the nearby Myakkahatchee Creek Environmental Park, where television news reports showed numerous law enforcement vehicles arriving and a tent set up inside the woods.
The location is where a Ford Mustang that Laundrie drove to the wilderness was found.
Laundrie is charged in a federal Wyoming indictment with unauthorised use of a debit card, which would allow authorities to arrest him if he is found alive.
It alleges Laundrie used a Capital One Bank card and someone’s personal identification number to make unauthorised withdrawals or charges worth more than 1,000 US dollars (£725).
It does not say to whom the card belonged or what type of charges were made.