The FBI's Denver field office released a statement saying that "a comparison of dental records confirmed that the human remains found at the T. Mabry Carlton, Jr. Memorial Reserve and Myakkahatchee Creek Environmental Park" were of Laundrie.
The partial human remains recovered at the environmental park where Laundrie was last believed to have been a day ago were described as "skeletal," a North Port police spokesperson had confirmed to News 4 earlier in the day. Two senior law enforcement officials also told NBC News that the apparent human remains found during the search included a portion of a human skull.
The Laundrie's family attorney released a statement from Brian's parents, Chris and Roberta, saying that they "have been informed" of the FBI's determination that the remains were indeed of their son.
"We have no further comment at this time and we ask that your respect the Laundrie's privacy at this time," the statement from attorney Steven Bertolino said.
Outside the Laundrie home in North Port, people continued to stop by with flowers and notes reading "Justice for Gabby."
"I'm sure every parent out there knows that getting the getting the news that your child is no longer with you is sad, under any circumstances," Bertolino told NBC News' Tom Llamas. "The fact that the Laundries have been subjected to these people out in front of their house for the last four weeks, and they continue out there today, it's just making all the more difficult."
An attorney for the family of Gabby Petito — Laundrie's fiancée who was found dead near a national park in Wyoming after a weeks-long search — said that the family would not make a statement at this time.
"Gabby's family will make a statement at the appropriate time and when they are emotionally ready," Rich Stafford told NBC New York.
The cause of death for Laundrie is not yet clear.
The FBI field office in Tampa confirmed the basic findings at a news conference Wednesday where for the first time in their six-week probe they called Laundrie a person of interest in Gabby Petito's murder, not just in her disappearance.
In addition to the human remains, the FBI said investigators found a backpack and a notebook believed to belong to Laundrie near a path at the Myakkahatchee Creek Environmental Park. The agency added that up until recently, the items were underwater, and were only found now that the water had receded -- an investigative boon Bertolino had suggested would help search teams two weeks ago.
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FBI teams will likely be on scene processing potential evidence for several days, officials said, and the park will remain closed to the public until further notice. The Tampa FBI office said that the Denver team is leading the investigation.
Bertolino initially said Chris and Roberta Laundrie were the ones to discover the items off a trail their son used to frequent. The discovery came just a day after the park reopened to the public, sparking questions about why the parents had gone there Wednesday and how they could have stumbled on a discovery trained investigators had been trying to make for the better part of the last five weeks.
Bertolino sought to answer those questions late Wednesday. He explained that Chris and Roberta Laundrie had wanted to go to Myakkahatchee Creek Environmental Park to search for their son and went the day after it reopened.
"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," he said.
"This is the very area of the park that we initially informed law enforcement on, I believe it was September 17th, that Brian would be most likely in the preserve in this particular area as I know it, near the bridge," Bertolino continued. "If that water had cleared two weeks ago, perhaps could have circled back and looked again. Perhaps they meant to. Perhaps they were further, deeper into the park and never got back to this park because it is so near the entrance, Chris and Roberta went to this area first, and as happenstance was, they stumbled upon these items."
It's not clear what if anything could be recovered from the notebook or what more the FBI might be able to glean from the items found in the environmental park, to advance their investigation into both Petito's death, and now Laundrie's as well.
Laundrie's death brings the nationwide search for the only person of interest the FBI had named in Petito's case to a dramatic end. He hadn't been seen since Sept. 13, when his parents told authorities their son said he was going for a hike in the Carlton Reserve. The silver Mustang his parents said he drove to the environmental park lot had an "abandoned vehicle" tag that was timestamped 2:24 p.m. Sept. 14, NBC affiliate WFLA previously reported.
That notice would have suggested the vehicle had been left there for at least a day before it was tagged. It'd be another few days before it would've been towed. It wasn't until Sept. 17 that Laundrie's parents reported him missing.
Petito's family didn't immediately comment on Wednesday's findings but previously said they hoped Laundrie would be found alive, because without him they feared they may not ever get complete answers as to what happened to their daughter.
The 22-year-old Long Island woman's remains were recovered Sept. 19 in a remote area of a Wyoming national park she and Laundrie had visited during their months-long cross-country road trip.
Last week, the county coroner who ruled Petito's death a homicide revealed chilling details from the autopsy results: She was strangled by someone's bare hands, and likely died three to four weeks before she was found.
That type of death is one of "the most intimate of homicides that can occur," forensic expert Joseph Scott Morgan told News 4's The Debrief podcast last week.
LISTEN TO THE PODCAST: WHAT GABBY PETITO'S AUTOPSY DETAILS COULD MEAN -- AND WHY 'THE VANISHED' TEAM THINKS THIS CASE STOOD OUT
The coroner who examined Petito's remains, Dr. Brent Blue of Teton County, declined to share additional details on the autopsy results, citing state protocol. The FBI did not comment publicly on those autopsy results or lend any public insight as far as what they might mean for the direction of their investigation.
The FBI continues to solicit tips by phone and online regarding the case.