The FBIis still analysing what investigators have described as'potentially critical DNA'at its lab in Quantico, Virginia, as the search for missing Arizona grandmother Nancy Guthrie reached the100-day markon Tuesday. Guthrie, 84, the mother of Today presenter Savannah Guthrie, disappeared from her home near Tucson in the early hours of 1 February, and no suspect has been publicly identified.

The case has drawn sustained attention in the United States because of both the mystery surrounding her disappearance and her daughter's public profile. The Pima County Sheriff's Department initially sentDNA evidence collected from Nancy's hometo a private laboratory in Florida. Weeks later, local authorities transferred the material to the FBI crime lab in Quantico, where testing remains under way, according toCBS News.

Investigators are withholding details of the DNA, including what was recovered and where it was found inside the Tucson-area property. Law enforcement sources told CBS that the analysis remains active atQuanticoand that the sample is being treated as a priority.

Former FBI supervisory special agent Lance Leisingexplained why the location of DNA inside a victim's home can matter so much. He told CBS that 'an item containing DNA such as a strand of hair found somewhere in a house is one thing, but a strand of hair near the victim's last known location, such as in her bed, would be a high priority for the FBI'.

Another retired FBI supervisory special agent,Jason Pack, warned against expecting a quick result shaped by television crime dramas. He said DNA analysis can involve painstaking work, including building family trees to help narrow down a possible suspect. That process, he added, 'takes far longer than television crime dramas would have people believe', and 'that kind of work is slow because it has to be right'.

Those comments underline a central problem in the case. The most talked-about piece of evidence is also the one the public knows least about. Officials have not said whether the DNA belongs to Nancy, a relative or an unknown individual, nor whether it has already generated investigative leads. At this stage, its exact significance remains unclear.

No suspect has been identified publicly, but a masked man captured on Nancy Guthrie's doorbell camera around the time she vanished has become a major focus of public attention. Authorities have not released a detailed description of the man or said clearly whether they believe he is directly connected to her disappearance.

Pima County SheriffChris Nanos, whose handling of the case has faced criticism from some observers, has refused to discuss the DNA evidence in detail. Speaking to CBS by phone on Monday, 11 May, he said talking publicly about specific evidence could damage any future prosecution.

'It would be highly inappropriate of me to speak to the evidence. We have to keep the integrity of this case,' Nanos said. 'If we make an arrest, that individual has the right to a fair trial, [so] I can't sit here and address all of that.'

The sheriff insisted that his office and its partner agencies remain focused on resolving the case. 'We are working hard with all of our partners to resolve this case, and we will,' he told the outlet.

Source: International Business Times UK