"A Thousand Splendid Suns" by Khaled Hosseini

While the first three parts of the novel are written in the past tense, the final part is written in present tense. What do you think was the author's intent in making this shift?  How does it change the effect of this final section?

For a biography of the author, Khaled Hosseini, check out:

http://www.achievement.org/autodoc/page/hos0bio-1

For further information about the author, his other books and a fascinating interview, check out: 

http://khaledhosseini.com/