Here's why:
* Copyright Term: Copyright in the United States typically lasts for the life of the author plus 70 years. Agatha Christie died in 1976.
* Public Domain: This means that most of her works will enter the public domain in 2047 (70 years after her death).
* Exceptions: There are some exceptions:
* Works published before 1923: Some of Christie's early works published before 1923 might be in the public domain, as copyright law was different at the time.
* Individual works: Some individual works might have been transferred to other publishers or their rights might have been handled differently.
* Adaptations: Adaptations of her works, like movie scripts, might have separate copyrights.
Therefore, while the majority of Agatha Christie's works are still under copyright, some individual works might be in the public domain, and there might be differences in copyright status depending on the specific work and adaptation.