From the Washington Post's report on the leaked Afghan documents:
"One report from the spring of 2007 refers to witnesses who saw what appeared to be a heat-seeking missile destroy a CH-47 transport helicopter. The Times first unearthed the document in its review of the files. The Chinook crash killed five Americans, a British citizen and a Canadian. Even though the initial U.S. report stated that the helicopter was "engaged and struck with a missile," a NATO spokesman suggested that small-arms fire was responsible for bringing down the helicopter."