The 56-year-old Haggis, who won an Oscar in 2005 for co-writing "Crash," said he was quitting the church after 35 years.
The letter, dated Aug. 19, was published on a blog about Scientology and has since been widely circulated online.
Ziggy Kozlowski, a publicist for Haggis, confirmed that the director wrote the letter. Kozlowski said the letter was intended to remain private.
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