So they used scent dogs earlier on in the investigation and they did not pick up on Lisa's scent. That could be because she was carried and wrapped in a blanket.
However, if this man is carrying a baby with only a diaper on, Baby Lisa's skin cells would probably be falling as well. Right? You'd possibly think the scent dogs would have picked up on her scent where this man was walking with a baby.
Yes, if that was baby Lisa, why couldn't scent dogs follow the trail?