Nancy Guthrie Kidnapper Manhunt Is Being Examined in a New Way

The search to locate Nancy Guthrie's kidnapper is being looked at through a new lens ... it's not about tips or what we've seen of the abductor on camera ... it's about finding someone who fits that description -- who has been missing for 3 weeks.

Law enforcement sources connected to the investigation tell TMZ ... they want people -- especially in the Tucson area -- to think about who has gone MIA for the last 3 weeks, and there's now a fair amount of information that could help ID the kidnapper.

The man is somewhere between 5'9" and 5'10" with an average build and facial hair -- a mustache or a goatee/beard. If the ransom letters TMZ received are authentic, he's smart and very tech-savvy. Authorities believe he lives in the Tucson area.

The kidnapper has an Ozark Trail Hiker backpack, a coat we believe is an Athletic Works Fusion Knit jacket, a polyester holster, and a semi-automatic handgun.

Law enforcement wants to know who fits that description who has gone off the radar over the last 3 weeks.

Nancy was reported missing on Feb. 1 ... so the assumption here is the kidnapper hasn't been seen in public since then either.

Pima County Sheriff Chris Nanos says DNA crime scene evidence could be key to identifying Nancy's kidnapper ... but this is another way law enforcement is trying to find the perp.