"A team of 40 private investigators supervised by the
global firm, Kroll, Inc. worked for four months to capture
video of gun shows. Licensed as private investigators in
17 different states, these men and women have more than
460 years of combined law enforcement experience and
included many retired federal agents and police officers.
Participants were chosen based on their prior experience
conducting undercover operations and performance
in carefully constructed simulation exercises. Every
investigator who participated in the integrity tests was
required to complete an intensive training designed and
administered by Kroll. Investigators were also taught
how to properly use sophisticated video and audio
recording devices. Cameras were concealed in baseball
hats and purses and had lenses no larger than the tip
of a ballpoint pen. The synchronized audio recording
devices were concealed in watches."
http://www.gunshowundercover2009.or...site226/client/Gun_Show_Undercover_report.pdf