Though authorities have not explicitly connected Laundrie to Petito's death, they have said he was among the last people to see her alive. "Two people went on a trip, and one person returned," North Port Police chief Todd Garrison said in September.

With Laundrie now gone and many questions still unanswered, here's what experts say investigators could home in on to help them answer what happened to Petito.

Crime scenes will be critical in investigation

Among the most important components in an investigation like this are the crime scenes, said Paul Belli, a retired lieutenant of the Sacramento County Sheriff's Office and president of the International Homicide Investigators Association.

Teton County, Wyoming, Coroner Dr. Brent Blue said Petito died by manual strangulation/throttling, adding that her body had likely been outside in the wilderness for about three to four weeks before being found.

"Throttling means that someone was strangled by human force. There was no mechanical force involved," Blue told CNN.

There could be clues as to what happened -- and who did it -- that investigators may be able to collect from a crime scene, Belli said, including fingerprints, depending on the condition of the human remains. What's difficult in cases like these is that unlike killings that are committed by strangers of the victims, when the person of interest is someone the victim was involved with, finding their DNA on a victim's body is to be expected.

"You would expect DNA on either one of them from the other," Belli said. "But I mean, if there's DNA maybe where it shouldn't be, that could be kind of a clue as to what may have occurred."

"So there are ways to absolutely, at least get you to a point where you're like, 'OK, this definitely makes sense, this is the person who did this crime,'" he added.

The type of crime also can help offer hints, said former federal prosecutor Neama Rahmani. Killings involving manual strangulation can often indicate "an emotional element," Rahmani said.

Some key items could provide answers

Investigators last week recovered personal items such as a backpack and notebook along with Laundrie's remains. A source with knowledge of the investigation told CNN's Randi Kaye the notebook is "possibly salvageable." And experts say that could offer more insight.

Those items will likely be taken to an FBI lab where there are "experts who really spend their careers doing things like drying out paper evidence, trying to recover the writing and the ink marks and potentially fingerprints and all sorts of other potentially relevant pieces of evidence from an article just like this," former FBI Deputy Director and CNN senior law enforcement analyst Andrew McCabe told CNN's Wolf Blitzer Thursday.

The notebook could potentially include information like Laundrie's motives, his feelings about Petito and other notes he made about events in Wyoming, McCabe added.

Investigators also obtained a search warrant last month for an external hard drive they found in Petito's white van -- the one the couple used during their trip and in which Laundrie returned, alone, to their North Port home. Authorities have not shared details on what they found on the drive.

Finding phones in a case like this could also offer an "incredible amount of information," Belli said. A source close to the Laundrie family told CNN last month Laundrie left home without his wallet and without a cell phone he had purchased earlier in September. Police do not have the phone he had with him during the couple's trip, nor do they have Petito's phone, CNN confirmed earlier in October.

Finally, videos that authorities have collected of Laundrie and Petito could also help put together pieces of the puzzle in the couple's journey -- and perhaps Laundrie's journey back to Florida.

"I don't think people realize the sheer volume of information that we now get on every case," Belli said. "Video, phone records... if that vehicle had any information that can be gleaned from it with a GPS."

Laundrie was charged with using a debit card and PIN for accounts that did not belong to him after Petito's death, according to an indictment.

"(Authorities) probably collected video from wherever those were used, video for wherever he may have appeared to stop for a period of time. I doubt he drove completely straight through," Belli said. "So, there's a lot of additional work to be done that has been in progress, most likely."