Current and former staff of American not-for-profits with experience in North Korea have expressed doubts about key claims related to a “missionary spies” intelligence-gathering program that surfaced on Monday.

The program, said to have existed from 2004 to 2013, was claimed to have used a now defunct U.S. NGO to smuggle “scores of bibles” into North Korea in order to “test run” a smuggling route on behalf of the Pentagon, online outlet the Intercept reported on Monday.

Benefiting from in-country access facilitated by the Denver-based Humanitarian International Services Group (HISG), the Intercept said the U.S. Department of Defense used the NGO and its network to subsequently “move equipment into and