The search for Nancy Guthrie is far from over after the FBI released chilling doorbell camera footage showing a masked individual outside her front door on the night she disappeared. Ten days into the investigation, law enforcement's approach has likely shifted from a frantic "race against the clock" to what security expert Dan Donovan describes as a "controlled operation," he exclusively told Us Weekly. "The family's role is discipline, and the FBI's role is pressure - quiet pressure," Donovan, who is the Founder and Managing Partner of Stratoscope Holdings, a security and risk management firm, explained to Us. Authorities were spotted in Guthrie's neighborhood on Tuesday, February 10, just hours before officials announced an "extensive search" along multiple roadways in the Catalina Foothills area near the $1 million Tucson, Arizona, home belonging to Today host Savannah Guthrie's missing mother. FBI Director Addresses Delay in Releasing Nancy Guthrie Surveillance Footage An FBI official told NBC News that tips have "dramatically increased" since the release of Nancy's Nest camera video footage and photos on Tuesday, showing the first glimpse at a potential subject. The six black-and-white images showed a person walking up to the property, wearing a mask and gloves while carrying a backpack. The person attempted to cover the camera with their hand, also using plants pulled from the front yard to conceal their identity. At least one of the videos shows the masked individual with a holstered gun. FBI Nancy was dropped off at her home on the night of January 31 and was reported missing around noon the following day, on February 1. "At this stage, investigators should be working the case like a signal hunt: reprocessing evidence, building timelines, tracking vehicles and digital footprints, and following up on inconsistencies," Donovan told Us. As a nationally recognized expert in high-risk security operations, protective strategy, and threat mitigation, Donovan pointed out "the fact that searches are being repeated is not unusual - it often means law enforcement has developed a new theory and is verifying it." Days ago, authorities were seen searching a septic tank behind Nancy's home as the desperate hunt for clues continues. TMZ's Harvey Levin Details Contents of Alleged Nancy Guthrie Ransom Note Donovan told Us, "Septic tanks are searched because perpetrators sometimes use them to dispose of evidence." He clarified, "It doesn't automatically mean investigators believe she's there - it means they believe something important could have been hidden there." In yet another recent development, a man detained in connection with the disappearance of Nancy maintained his innocence after being questioned and subsequently released by police on February 10. The man said that after speaking to authorities, officials told him he was "free to go." Activity was also recently detected in a bitcoin account mentioned in ransom notes allegedly connected to Nancy's disappearance, according to multiple outlets. On February 5, the FBI confirmed two ransom deadlines mentioned in the unverified letters, the first of which was 5 p.m. local time that Thursday and the second set for the same time on Monday, February 9. "Typically, missed deadlines do not mean the threat has ended," Donovan told Us. "Ransom demands should still be treated as credible until definitively disproven."