Nancy Guthrie has been missing for 45 days, and with the latest update in the case being of little use to authorities, one expert tells CBS News the extended timeline means it "becomes much harder to keep the investigation going."

Law enforcement sources told CBS News that additional images were obtained in the last couple of weeks from surveillance cameras installed at Guthrie's Tucson home, where she is believed to have been abducted from in the middle of the night on Feb. 1.

The images, taken from a camera fastened to a fence and focused on the back of the house and another that showed the driveway and front of the garage door, captured family members, landscapers and pool workers stretching back weeks prior to the kidnapping. Nothing was deemed suspicious, and no images reviewed showed the suspect captured on the front door camera.

In the seventh week of the investigation into the disappearance of the 84-year-old mother of "Today" co-host Savannah Guthrie, doorbell camera video shared by the FBI on Feb. 10 remains the only known images of the suspect.

Lance Leising, a retired FBI supervisory special agent, told CBS News it all points to "a lack of meaningful leads. That's the initial thing it says to me."

"It becomes much harder to keep the investigation going, keep it current and fight for new leads," he added.

DNA recovered from the scene is still being analyzed, with investigators turning to forensic genetic genealogy in hopes of breaking the case open. It's a technique that's been used in the past to find other high-profile criminals, including Bryan Kohberger, the man who killed four University of Idaho students in 2022.

Leising warned, however, that the process "takes a while."

"Maybe you've got multiple people within the same DNA family that could potentially be suspects. You have to investigate each one of those independently," he said.

Authorities also continue to receive tips, with over 1,500 potential leads coming into the FBI after the Guthrie family announced a $1 million reward. But it's been nearly three weeks since the family last called on the public for help and more than a month since law enforcement held a news conference to discuss the case.

"I'd like to be hopeful that — and I'm sure the family is incredibly hopeful — that the silence is because they're on to something," Leising said. "They just need to investigate harder."

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