He told "GMA's" George Stephanopoulos that the family does not yet know his cause of death.
They hope to learn the findings of the Medical Examiner on Friday afternoon.
Bertolino said that they did not find out any new information yet from the items that were found near Brian's body.
"None at all. As you can see from some video that's circulating, it shows the white bag that was picked up by Chris Laundrie was almost immediately turned over to law enforcement. Law enforcement found the backpack. I do not know if the notebook was in the white bag that Chris picked up or if it was in the backpack that law enforcement picked up," he said.
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Apparently, Chris and Roberta Laundrie said Brian was grieving when he came home on September 13, but Gabby Petito's body wasn't discovered until the 19th.
"Brian had been extremely upset, Chris and Roberta were extremely concerned about him, they expressed that to me. That when he walked out the door that evening, they wish they could have stopped him, they wish they could have you know, prevented him from going out, but he was intent on leaving. Chris said to me, I know in hindsight I couldn't stop him, but I just wish I could have," he said.
As for how the family knew where to look, Bertolino said that Chris had hiked with Brian on several prior occasions and the area was too flooded to get off of the path during prior searches.
"Did Brian tell the Laundries anything about what happened to Gabby before he disappeared?" Stephanopoulos asked.
"George, that's not something I can comment on right now, and I'd like to just leave it at that," Bertolino said.
"Well, if you can't comment on it, that means you know something about it," Stephanopoulos said.
"Well, I think everybody out there knows that whether the family or myself have some information share, there's not that much that we can say at this point in time and I'm going to leave it at, no comment," Bertolino said.
"Is that because they've been cooperating with the FBI?" Stephanopoulos asked.
"George, I've been quite clear on this from the very beginning. When it comes to the FBI we have nothing to say in respect to the Gabby Petito incident. With respect to Brian, we've been cooperating since day one. And those are two different, from a legal perspective, those are two different scenarios, one was the missing persons with Brian, one was the missing persons with Gabby."
Bertolino concluded the interview by saying that so far, the Laundrie family had nothing to say to the Petito family. He had yet to speak to the Laundries Friday morning.
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The couple first met as teenagers on Long Island, New York, and more recently moved to Florida's Gulf Coast to live with his parents.
They first gained an online following while on their trip in a converted Ford Transit van in videos filled with happy scenes that may have concealed deeper problems. After Petito disappeared, the case became a true-crime obsession on social media.
The couple was stopped on Aug. 12 by police in Moab, Utah, after they had a physical altercation, but no domestic violence charges were filed. The police department there is conducting an internal review to determine if policy was followed.
Laundrie returned home alone on Sept. 1 in the van the couple took on their trip, which was later impounded by authorities. He was reported missing after telling his parents that he was going for a hike in the Carlton Reserve.
Her body was found Sept. 19 on the edge of Wyoming's Grand Teton National Park, which the couple had visited.
Teton County Coroner Dr. Brent Blue ruled her death a homicide and said she died by manual strangulation.
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Laundrie had not been charged in her death, although he was indicted for allegedly using two financial accounts that did not belong to him in the days following her killing.
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