Sandra Bullock (Linda Schell) was actually in New York City with her family, and witnessed the second plane, United Airlines Flight 175, crashing into the World Trade Center's South Tower on September 11, 2001.
The Questionaire that Oscar gives The Renter have fifteen questions on them. They are: 1. What is your full name? 2. What is your nationality? 3. What is your occupation? 4. What did your father do for a living? 5. What did your mother do for a living? 6. Were you ever married? 7. Did you have children? 8. Where have you traveled in the world? 9. How did you learn of the apartment for rent? 10. Did you ever know my father, Thomas Schell? 11. When you did speak, what other languages did you know? 12. Were you ever a soldier in a war? 13. Did you ever kill anyone? 14. Do you have any friends? 15. Why did you stop talking?
At age 82, Max von Sydow was nominated for an Academy Award for Best Supporting Actor for this film, becoming the second oldest man to be nominated for a male acting Oscar. von Sydow was aged 82 years and 289 days old, whereas the record holder was Hal Holbrook aged 82 years and 339 days old, and was nominated in the same category for Into the Wild (2007), beating him by just fifty days.
James Gandolfini filmed scenes as someone who meets Sandra Bullock's character at a grief counseling, but they were cut from the film due to a negative test audience reaction. His character was mostly likely Ron from the book.
Thomas Horn came to the attention of Stephen Daldry when, at the age of 12, he won 31,800 dollars on a "Kids Week" episode of the television series Jeopardy! (1984), that aired July 8, 2010 (a date Thomas mentions at 00:44 in the special feature "Finding Oskar" on the Blu-ray disc).
The scenes, involving the swing set, were shot in a part of Central Park called Cherry Hill. There are no swing sets, or any playground equipment, in this section of the park. It was added for filming, and then removed.
Second film related to the September 11 terrorist attacks to be nominated for an Oscar. The first was United 93 (2006). Both films were nominated for two Academy Awards and neither film won one. World Trade Center (2006) was not Oscar nominated, neither were September 11 (2002) or the more loosely related 25th Hour (2002).
The trivia items below may give away important plot points.
In an early draft of the script the Renter finally speaks at the end. Max von Sydow was opposed to it, since he felt the movie was about Oskar and it wasn't necessary to know whether or not the Renter recovers his speech. He was pleased that it wasn't in the completed film.
When Sandra Bullocks character confesses to Thomas Horn that she knew about his search, Horn asked how. She explains to him that when he got all the phone books from Stan the doorman to do a school project on census, she knew it was a lie, because the census wasn't for another seven years. Thomas Horn previously appeared on "Kids Week", on the television game show Jeopardy! in 2010. The Final Jeopardy question was "The first of these was authorized in 1790 'providing for the enumeration of the inhabitants of the United States'". To which the answer was census. Horn answered correctly which placed him in first with winnings of 31,000 dollars.