Project Snitchwalker

We found that ATF officials did not completely and accurately track information related to foreign national CIs, and as a result we were unable to determine an accurate total number of ATF-sponsored foreign national CIs. The inability to efficiently identify these CIs is especially problematic because these CIs often have criminal histories or are involved with criminal organizations, and therefore the risks associated with these CIs remaining in the United States without legal authorization are higher than normal. [More]

So we may not know about them until they're "found" at crime scenes...?