WASHINGTON, Aug 15 (Reuters) - Former intelligence contractor Edward Snowden began downloading documents describing the U.S. government's electronic spying programs while he was working for Dell Inc in April 2012, almost a year earlier than previously reported, according to U.S. officials and other sources familiar with the matter.

Snowden, who was granted a year's asylum by Russia on Aug. 1, worked for Dell from 2009 until earlier this year, assigned as a contractor to U.S. National Security Agency facilities in the United States and Japan.

Snowden downloaded information while employed by Dell about eavesdropping programs run by the NSA and Britain's Government Communications Headquarters, and left an electronic footprint indicating when he accessed the documents, said the sources, speaking on condition of anonymity.