cleanskin
n.— «The Times said that at least two of the men had just returned from Pakistan, but none were on the files of security services. This meant they were “cleanskins”—intelligence parlance for terrorists with no previously known link to suspicious groups, and thus incredibly hard to track down before they strike.» —“Model citizens, ruthless killers” in London, England TodayOnline (Singapore) July 14, 2005. (source: Double-Tongued Dictionary)
Further reading
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