TUCSON, Ariz. — As a growing memorial outside Nancy Guthrie's Tucson-area home continues to draw visitors, new questions are emerging about whether investigators are monitoring the site. Guthrie, the 84-year-old mother of "Today" co-host Savannah Guthrie, is believed to have been abducted from her home in the early hours of Feb. 1."They could [have eyes on the memorial], we're just not seeing it," Betsy Brantner Smith, spokesperson for the National Police Association and a retired police sergeant, tells Fox News Digital. "They could be keeping track of it, but we're not seeing the cameras."FORMER FBI AGENT OFFERS NEW THEORY ABOUT NANCY GUTHRIE'S DISAPPEARANCE: 'PERSONAL GRIEVANCE'Yellow flowers, handwritten notes, artwork and even an open letter addressed to the "kidnapper" have been left at the makeshift tribute in front of her home.While the memorial grows, however, visible law enforcement presence has significantly dropped."Detectives are reviewing all viable leads in this case," a spokesperson for the Pima County Sheriff’s Department told Fox News Digital. "We do not speak to specifics, as this is still an ongoing investigation."Authorities have not publicly identified a suspect, vehicle or any persons of interest.MULTIPLE SUSPECTS ARE POSSIBLE IN NANCY GUTHRIE'S ABDUCTIONHaunting Nest doorbell camera video shows a masked man on Nancy Guthrie's front steps around the time of her abduction. He is described as being of average height and build and was wearing a black Ozark Trail backpack."In this type of situation where you have the potential for a suspect having done this because he or she is somehow obsessed with Savannah Guthrie or seeing Nancy featured on the ‘Today Show’ multiple times… someone who is obsessed with notoriety, celebrity — there's a lot of pathology involved in that," Brantner Smith said.FOLLOW THE FOX TRUE CRIME TEAM ON X"Potentially, that is the type of person that could come back to the memorial, look at the memorial, even take photos of the memorial and add to the memorial themselves."As to why there's been an alleged lack of law enforcement presence monitoring the site, Brantner Smith pointed to one likely scenario.SIGN UP TO GET TRUE CRIME NEWSLETTER"It may be because they have solid suspects, and they just haven't released that information to the public," she said. It's not uncommon for an offender to return to the crime scene, she added.SEND US A TIP HERE"Sometimes the offender will come back to the scene of the crime. So, in that vein, they would come to the memorial, and they may have left their own note, their own flowers," she said.Often, it's a mark of their arrogance, she told Fox News Digital."I am guessing that the suspect or suspects who did this are frankly taking great pride in the fact that so far they've got away with it," she added. "Coming back can also be a way to bring back that rush that they had when they originally committed the crime."LISTEN TO THE NEW 'CRIME & JUSTICE WITH DONNA ROTUNNO' PODCASTSuch behavior happens frequently in arson cases, she said. "But it's also not untypical in a homicide case or, in this case, a missing person," she continued. "We've got to look at the psychology of people who do this kind of stuff. They also may want to come back to see what kind of people are leaving notes, and leaving flowers."For that reason, she said, investigators should be reading the notes to develop potential leads."They're coming back to see the impact that they had on this neighborhood and on this family," she said. "And the rest of us would view that as very sick, but law enforcement has to view that as a way to collect clues."LIKE WHAT YOU'RE READING? FIND MORE ON THE TRUE CRIME HUBSavannah, her sister Annie, and brother-in-law, Tommaso Cioni, placed flowers at the growing tribute near the foot of Nancy’s driveway on Monday in a somber visit to the crime scene.A combined reward for information that leads to Nancy's recovery from the FBI, local authorities and the Guthrie family stands at over $1 million. It has not yet been claimed.Savannah is asking anyone with information to dial 1-800-CALL-FBI.