After 50 years, the Pentagon Papers give up their final secrets

Journalist behind scoop reveals how he tricked whistleblower to get copies of explosive Vietnam war reports

It is to many the greatest journalistic scoop in a generation - the publication of a 7,000-page government report that laid bare how successive US administrations had escalated the Vietnam war while concealing doubts that the action could ever be successful.

That report - the Pentagon Papers - was made public in 1971 by the New York Times over legal objections by the Nixon administration. But the manner in which the documents had been obtained by Times reporter Neil Sheehan has always been a mystery.