Search Intensifies: FBI agents are combing roads near Nancy Guthrie’s home as a man detained in the case publicly insists he wants to clear his name — but what are investigators really looking for?

As authorities comb through thousands of tips in the search for Nancy Guthrie, the missing 84-year-old’s home could still be providing leads for investigators to follow. Blood stains on the porch – which officials confirmed are Guthrie’s – suggest ways her kidnapper may have left traces behind, a forensic expert says.

“Blood is very sticky … if she’s leaving that blood stain on the step, I’m sure there was blood inside the house, which is wonderful for footwear,” former police detective Mike McCutcheon told CNN’s Laura Coates.

“You step in that, because you’re dealing with her, you’re in close proximity, you’re leaving those foot impressions behind,” McCutcheon said, noting forensic investigators have methods such as spraying certain chemicals to highlight traces of this type of evidence.

McCutcheon said the blood stains on the porch also give investigators insight into what happened.

“I would not be able to tell you how she was taken, but what I can tell you is that those are drip stains,” McCutcheon said, noting the relatively large size and uniform shape that suggests the blood was “falling at ninety degrees.”

“If it were an impact stain, blood coming off from a weapon … you’re going to have smaller stains and they’re going to have some direction. So there was some altercation that was in there that caused her to bleed, and that we can’t determine.”