(NewsNation Now) — A fourth week searching Florida’s Carlton Reserve for Brian Laundrie yielded nothing.

Friday, police in tactical gear and wearing camo were in the swamp for several hours, and then packed up and left. They were armed with assault rifles. North Port Police officials said the officers were continuing to search for Laundrie, but also conducting training at the same time.

Laundrie has not been seen since he left to go on a hike in the reserve Sept. 13, according to his parents. He is wanted on an indictment on a bank fraud charge for using the debit card of his girlfriend, Gabby Petito. He’s also a person of interest in her disappearance and death.

The search for Laundrie began Sept. 17, four weeks ago, when his parents told investigators they had not heard from him in days. Dozens of tours through the reserve have not appeared to give police much to go on.

“I think the real bottom line is, how much more time will they spend in the swamp in the woods, doing these walks?” said Bill Proctor, a private investigator, on Friday’s “NewsNation Prime.”

Dennis Frank, a 22-year veteran of the FBI, said police could have clues they have not discussed publicly.

“I have to think they’re not relying on just information that he might be there,” he said on “NewsNation Prime” on Friday. “There has to be some kind of information that they’re getting … that tends to point them in that direction, because they are expending a lot of resources in that area.”

Petito’s body was found outside Grand Teton National Park in Wyoming on Sept. 19, and was identified two days later. Coroner Dr. Brent Blue said she was strangled to death and her body was left outdoors for three to four weeks before she was found.

The Laundrie house was quiet most of the day until Christopher Laundrie, Brian Laundrie’s father, was spotted outside the front door with a power drill. He installed a Ring camera outside as more neighbors showed up with signs for the front lawn.

One reads “What if it was Cassie?” referring to Brian Laundrie’s sister, Cassie Laundrie.

The Laundrie parents have stayed quiet since the investigation began. Cassie Laundrie told a group of protestors outside her home earlier this month she was frustrated with her parents’ silence, but she did not know any more than what was in the news.

Gabby Petito’s father, Joseph Petito, posted a photo on Twitter from Wyoming on Friday afternoon with the caption, “I now know why you came here. #gabbypetito has a beautiful view from now on. Love you, and miss you.”