How a mother-daughter duo built a $15 million con

Federal Investigators say it was one of most planned and intricate cons they've ever seen.

The swindlers, a mother-daughter team, used disguises, a phony headstone and even a baby to sway their victim—the sole heir to a family tree farm fortune, according to investigators.

Donna Maddux, assistant United States attorney, District of Oregon, tells CNBC: "It was incredible dedication. But the payoff they knew they had at the end was even more incredible."

Maddux says the con artists built trust with the victim over years and wound up stealing at least $15 million.