and then there's guillermo vasco, the young husband who married a pretty doctor from massachusetts. and what you're watching is the surveillance video of him about to hire a hit man to kill his wife. >> my wife betrayed me. >> i'm gonna make it look like she disappeared. >> exactly. >> he wants her killed and buried ten feet under. >> how soon did he want her dead? >> as soon as possible. >> do you want it to be painful or do you want it done quick? for her. it's your money. >> yeah, yeah. >> reporter: ken is the hitman hired by guillermo and tonight he's not the only one coming forward. a group of his comrades, all men hired to kill, boarding planes, getting into their cars and on their way to sit down exclusively with "20/20." but these men all have a secret. they are undercover federal agents with the atf posing as hit men. they meet us at atf headquarters in washington, d.c., where we have makeup artists waiting. >> just this morning. >> they sit down to have their appearances completely changed. >> i'm feeling my feminine side coming out. >> oh, there's nothing feminine about t