Prisoners - I didn't understand some things

Hello.

When they find the first girl (affroamerican girl) and she wakes up and see's Keller, the girl says "You were there" and then the image of a man with green hoddie jacket carrying the affroamerican girl. Then Keller runs in his truck and goes to the aunt´s house. Why the girl said so? And why at the end of the movie, Keller's wife says to the detective that her daughter asked for a whistle because she said that she found the lost whistle in that ground? Who put the whistle there? Keller?

Thank you in advance! :D