>> reporter: crystal, a mother of two young sons, told weldon her husband was violent and abusive. she said she wanted to buy a gun for protection. >> so at that point, i asked her, "are you prepared to kill him?" because that is a very real possibility. you know, "if it's his life, your son's life, or your life, then you have to make that decision." and after a few moments, she said, "yes, if i have to." >> reporter: weldon took crystal under his wing, taught her to defend herself even in stressful situations. >> this guy sounds like he was actually looking out for you a little bit? >> yeah. somebody who's in the business of saving lives and, you know -- a warrior and a hero and that type of mentality, yeah, he wanted to help me. >> reporter: at home, crystal also helped herself, used a mini cassette recorder to gather evidence against her husband. >> oh, god. stop. please,