samantha fleming and daughter serenity were last seen in anderson , indiana on april 5 .
the three-week-old infant was discovered unharmed in the gary , indiana home where the body of a young woman was discovered .
the alleged kidnapper was not at the home , which had a nursery .
alleged kidnapper 's neighbor said the woman had told her she was pregnant with twins but that one had died during birth .
the child was in the care of the alleged kidnapper 's sister when police arrived after fleming 's wallet was found nearby .