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.
"Throttling means that someone was strangled by human force. There was no mechanical force involved," Blue told CNN.
"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.
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,"
"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."
"(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," "So, there's a lot of additional work to be done that has been in progress, most likely."
“It's a very, very strong circumstantial case," “You have a history of violence between the two. You have all evidence that indicates (Laundrie) was the last person to see her alive and the manner of death, that manual strangulation, that tends to be... most often someone you know."
“Did they help him escape? Did they help destroy evidence?" Palm Beach County, Florida, State Attorney Dave Aronberg told CNN's Wolf Blitzer Friday night. "What did they know?"
“Though with Laundrie deceased it may be harder to find the answers that both investigators and the families were hoping for, there may still be a lot that could be done in the investigation into Petito's killing”
"I mean the closure is really, did he do it or did he not do it, that is going to be the overarching feeling based on my experience," “The investigators," he added, "I guarantee that they feel a great need to provide the truth, whatever that truth is, to both sides of the family. That's really what we do as investigators is find all the facts and lay out the truth."
Gabby Petito investigation: What happens now that Brian Laundrie is dead - CNN
*Including for possible relevancy:
https://www.ojp.gov/pdffiles1/nij/grants/248770.pdf
A Trial Lawyer's Guide to Surreptitious Audio Evidence on JSTOR