Elizabeth Smart talks to the media outside the Federal Courthouse after addressing her kidnapper, Brian David Mitchell, during his sentencing in Salt Lake City, May 25. (Michael Brandy/Reuters)

Calling Brian David Mitchell's crimes against Elizabeth Smart “unusually heinous and degrading,” U.S. District Judge Dale Kimball said that “a life sentence reflects the seriousness of the crime.”

Smart, who at 23 has become an activist for missing children, addressed Mitchell outside the courthouse Wednesday. Mitchell was unresponsive except to sing a string of hymns. Smart said:

Brian David Mitchell is escorted into the Frank E. Moss Federal Courthouse in Salt Lake City. (Jim Urquhart/AP)
I don't have very much to say to you. I know exactly what you did. I know that you know what you did was wrong. You did it with a full knowledge. I also want you to know that I have a wonderful life now, that no matter what you do, it will not affect me again. You took away nine months of my life that can never be returned. But in this life or next, you will have to be held responsible for those actions, and I hope you are ready for when that time comes.

Although Mitchell would not look Smart in the eyes or offer her an apology, Smart said she didn’t care.

I heard enough during those nine months, and I never have to hear anything again.

After Smart was discovered in Sandy, Utah, in 2003, she recovered from the ordeal surprisingly quickly, with her father calling it a small “miracle” that she was starting to act like a normal teenager.

Smart continued to try to lead a normal life, attending Brigham Young University for college, where she studied music as a harp performance major, and then moving to Paris in 2009 to go on a Mormon mission. (She is a member of the Church of Jesus Christ of Latter-day Saints.) Smart says she may consider law school next.

But Smart has also decided her experience will lead her to a life of work in child advocacy. In 2006, she went to Congress to support Sexual Predator Legislation, and in 2008, she presented a book published by the Department of Justice called You’re Not Alone , about children who had gone missing but been recovered.

Smart does much of her work through the Elizabeth Smart Foundation, which she founded to help children nationwide.

“Today is the ending of a very long chapter and the beginning of a very beautiful chapter for me,” she told crowds outside the courthouse Thursday.

Watch Smart’s remarks after the court case:

Watch an interview with Smart a few days before the trial: