Well I'm not saying the document is not true. But NY Times didn't confirm. NY Times just said: " Somebody said so, blablabla..."
Whether this document is true or (more likely IMO) a fake, I find it comical that the number of bitcoins allegedly lost over a few years is 744,408. An organization that failed to notice the disappearance of half a billion dollars, millions of dollars per employee, nevertheless is supposed to have been able to calculate their losses to an accuracy better than 1 part in 105.
Document is true, as confirmed by NY Times:
http://www.nytimes.com/2014/02/25/business/apparent-theft-at-mt-gox-shakes-bitcoin-world.html?_r=0A document circulating widely in the Bitcoin world said the company had lost 744,000 Bitcoins in a theft that had gone unnoticed for years. That would be about 6 percent of the 12.4 million Bitcoins in circulation.