Here's two:
John Jamelske, serial rapist-kidnapper in New York state.
http://en.wikipedia.org/wiki/John_Jamelske
Austrian Josef Fritzl after two decades of holding his daughter and many of their children captive in a secret basement took one out to go to the hospital when she was very ill. He brought 2 or 3 children to live upstairs as babies and claimed that his daughter had abandoned them on his doorstep.
http://news.bbc.co.uk/2/hi/europe/7371959.stm
ETA: additional info. Jamelske was caught only when his 5th known victim was able to call her sister. After being held for 6 months, he took here out twice. The 2nd time she was able to get to a phone and call her sister, which set of events that culminated in her rescue.
Jamelske held 2 girls and 2 women captive in a series of kidnappings before that. The earlier victims ranged in age from 14 to 53. Some were kept 6 or 9 months and one for two years. He eventually released each one. At least one wrote a letter home saying she was in rehab. The first victim, who was 14, did not report her kidnapping to police when she was released. The others did but their reports were not investigated aggressively.