CIA contractor Edward Snowden, who leaked some of America's most closely guarded secrets, had travelled to India before 2011 but did not report the trip during his background-check process.
"The background checkers failed to verify Snowden's account of a past security violation and his work for the CIA, they didn't thoroughly probe an apparent trip to India that he had failed to report," the Wall Street Journal reported, quoting a review after leaks of classified documents by him.
During the 2011 routine background check that the National Security Agency contractor needed to keep his security clearance, the checkers didn't get significant information from anyone who knew him beyond his mother and girlfriend.
"The background interviewers learned from a work supervisor that Snowden had travelled to India, which Snowden hadn't reported during the background-check process, but the final background report failed to clarify the purpose of the trip," the Journal reported.
India was among over a dozen nations approached by 30-year-old Snowden for asylum while he was stranded at the Moscow airport. New Delhi had turned down his request.
The review report said several aspects of the background check did not meet the requirements of a 1997 document that outlined federal standards for background checks.
The most recent background check of Snowden was "so inadequate that too few people were interviewed and potential concerns weren't pursued," the Journal said.
National Counterintelligence Executive Frank Montoya Jr, who led the review, said the 2011 background check by a private contractor "did not present a comprehensive picture of Snowden," the Journal said.
After the background check renewed Snowden's high-level security clearance, he had access, through his job at Booz Allen Hamilton, to top secret documents about US surveillance programs.
Snowden has argued he was acting out of conscience because he wanted to shine a light on a surveillance apparatus which he believes is out of control.
He is wanted on felony charges by the United States, but Russia has refused to extradite him.