that information led them to virginia tech freshman david eisenhauer and natalie keepers. >> she saidpath and she was a sociopath in training. >> reporter: david eisenhauer is charged with murder and abduction. keepers as an accessory. >> i hope everybody learns from this. because it can happen to you. >> reporter: what happened to elizabeth sirochin, 15, serrified her parents. she had been chatting online with a 30-year-old man. >> this guy wants to kidnap my daughter tonight. >> reporter: the sirochins, with the help of a friend, a former special forces vet, set a trap for the predator. >> i said, "do not move or i will shoot you!" >> ninan: peter's report "killer app" is part of a "48 hours" double feature tonight on cbs. up next... what a long, strange and lucrative it's been for this legendary guitar. othpaste that s prevent bleeding gums. if you spit blood when you brush or floss you may have gum problems and could be on the journey to much worse. help stop the journey of gum disease. try new parodontax toothpaste. ♪ essential for him, but maybe not for people with rheumatoid ar