Why the trail went cold in Nancy Guthrie case

"There was absolutely no reason to release that crime scene," said Joseph Giacalone, retired NYPD sergeant, adjunct professor at John Jay College of Criminal Justice and the author of a textbook about criminal investigation now in its fourth edition.

"That entire house, the property, should have been cordoned off. No one should have stepped foot in that location other than law enforcement, and only for the purposes of doing the investigation."

Even if arrests were made in the future, he said, possible crime scene management issues mean "everything is going to be questioned" by the defence.

Mishandling a crime scene drastically reduces the odds of solving a case, he added.

Sheriff Nanos has alternately denied and admitted to mistakes. At a 5 February press conference, he said he'd have preserved the crime scene longer if given another opportunity.

"I probably could have held off on that," he said, adding: "We got what we thought was complete."

But Nanos has been embattled throughout the investigation, not just by criticism surrounding the Guthrie case. Local media have delved into his past - he had received written reprimands in El Paso, according to documents obtained by the Arizona Republic.

When contacted by the outlet, Nanos responded on 9 March: "That's your 'urgent' request? You sure you don't want to go back to my high school and ask why I got swats from the principal? Good luck with your hit piece."

The following month, the Pima County Board of Supervisors demanded answers from the sheriff who submitted written responses through his attorney, according to Arizona media. The board later voted not to remove him but Supervisor Rex Scott said the sheriff needed to repair a lack of trust in his leadership.

As investigators soldiered on, the global interest in the case, and the celebrity of Guthrie's daughter, likely didn't help matters, experts said.

"The fame probably drove the kidnapper underground, realising that there was a massive manhunt," said PI Ribacoff, who speculated that Guthrie probably died early on, prompting suspects to dispose of her body.

Other theories differ. Smith, for his part, is dubious about the veracity of the ransom notes - and believes Guthrie was ferreted down to Mexico where she could more easily be kept out of sight.

Nanos, meanwhile, told BBC News early on that he was confident Guthrie would eventually be found - whether it took "10 days, 10 months or worse." Nearly 40,000 tips had already poured in by February, he said, and the sheriff has stood by his commitment to solving the crime ever since.

And the eyes of the world remain riveted to the case - while global sympathies remain with Guthrie's family. They continue to offer a $1million reward and plead for tips.

Savannah Guthrie, after details of the two notes became public this week, renewed her appeals during a tearful segment on her NBC morning show.

"I just want to take the opportunity to ask people, really to beg people, to come forward," she said. "Somebody knows something."