TAMPA, Fla. (WFLA) – In a case of the magnitude of 22-year-old Gabby Petito involving multiple states, cities and locations, where do detectives begin?

Investigators describe this case as unraveling a mystery with many pieces to this puzzle.

It’s a case that began in New York state as Petito and her fiancé set out on a cross-country road trip with her fiancé Brian Laundrie.

However, police say Laundrie returned to North Port in her white Ford van and she is nowhere to be found.

“It is a mystery in the truest sense because you have no idea. You can’t go into a situation like this assuming you know how it’s going to play out because, really, you don’t,” said private investigator, John Allman.

The 51-year-old knows a lot about cases like these, working with law firms and law enforcement for more than a decade.

He says, right now, one of the biggest questions that needs answering is what was the mindset of Gabby when she was last seen.

“By trying to understand the mindset of an individual when they were last seen by people is critical because it can tell you if they have been looking to escape, to go somewhere by themselves,” Allman asked.

The former investigative reporter also knows that in asking the question, where’s Gabby, there are many possible answers.

“The goal is always to just locate the person that has gone missing. you hope that they’re safe, and they just needed to step away for a minute,” Allman explained.

He tells 8 On Your Side, in a case like this, investigators typically begin at the end and start with the last place a person was seen, then backtrack.

Former federal prosecutor Stephen Crawford agrees.

“Law enforcement gets to a position where they know who did it, but then they’ve got to figure out how to prove it. And, that’s where they are,” Crawford said.

The longtime Tampa attorney, now in private practice, says there’s a lot of work for detectives.

He also said since Gabby’s fiancé is simply a person of interest and has hired an attorney, the young man cannot be compelled to talk.

“This is a case that if it turns out, unfortunately, the way it’s looking, it’ll be prosecuted locally wherever they find what they find,” said Crawford.

Amid all the uncertainty, questions and theories in the case, both men say their hearts go out to both families and hope Gabby is found safe.