Investigators went door to door, many times, requesting video. So they collected it all. If there was ANY EVIDENCE of Gannon, walking around the neighbourhood, LE would have released it immediately.
The whole purpose would be to get the public's help with where he went next. Every time a missing child is captured on video footage, it is always released so the public can see where and when they were last seen, and maybe someone will remember being there, and help solve the mystery.
The locals have a neighbourhood forum, where they meet to discuss issues like lost and found pets, and driveway car breaks ins, etc. They all checked their cameras and no one saw Gannon that afternoon.