As the story continues to unfold about what happened in cleveland, we're reminded how often ordinary citizens, neighbors, see something that solves a crime and saves a life. Abc's dan harris now on crimes solved by little clues. And he's asking, if you saw them, what would you do? Reporter: This modest house at 2207 seymour avenue -- were there missi clues here? And if you had seen them, what would you have done? For ten years, right under your nose. Wow, it's heartbreaking, actually. Reporter: Vigilance from everyday citizens has made all the different in some major cases. People living near this small house in texas reported seeing the image of a young girl gliding past a window. Child protective services found 9-year-old victoria kept hidden and in squalor by her own mother. Then there was what an 11-year-old boy named matthew dixon saw in the woods in oregon. Another young boy walking with a man matthew found suspicious. Well, when he said he was hunting and he didn't have a gun with him. It just seemed odd. Reporter: He later told his mom to call the cops, which led police to take out the kidnapper and rescue young tanner kahn. And of course there was the campus police officer at the university of california berkeley, who spotted phillip garrido handing out religious literature with his two daughters. I just got a weird, uneasy feeling. I was looking at the younger daughter, who was sitting across from me. And she was staring directly at me. It was almost like she was looking into my soul. Reporter: That hunch led to the discovery off jaycee dugard, kidnapped and help captive for 18 years. Today the fbi and advocates for missing chilen told us they don't want to encourage false accusations, but americans should report things that don't seem right. And if police don't respond aggressive, be persistent. We'd rather follow a thousand blind leads for the one occasion that we do find something that may help rescue a child. Reporter: Tonight there are thousands of long-term missing children's cases, cases that can be cracked open by one alert american, seeing something, and saying something. Dan harris, abc news, new york