Natalia Grace Adoption Story in the documentary reveals how the Indiana couple got deceived by the girl. Barnett family adopted her on April 26, 2010.

Natalia was believed to be a 6-year-old girl when Michael and Kristine Barnett atook her in.

Grace had lived with a few foster parents before finding her home in the Barnett household, according to BBC. However, all the families returned her to the US Social Services after having troubles.

Soon after Natalia was adopted, her adoptive parents Michael and Kristine started getting suspicious regarding her actual age.

According to BBC, she showed mature behavior aligned to teens rather than 6-year-olds and her adoptive mother Kristine revealed Natalia had fully grown adult teeth and pubic hair which she discovered while giving her a bath.

However, Natalia's mature behavior was the least of the problems for the pair. Michael claims she tried to kill the entire family one by one. She would place clear thumbtacks on the stairs to hurt the family.

Natalia also tried to kill Michael's former wife Kristine (the pair divorced in 2014) by poisoning her coffee once and pushing her to an electric fence in another instance. She also threatened to kill the pair's three biological sons and bury them below their home's deck in the backyard.

Barnetts had enough torture and threat and decided to flee to Canada in 2014. The pair rented an apartment for Natalia in Lafayette, paid one year's rent and bought her food, and left her alone where she lived for a year before contacting the police.

Michael and Kristine were charged with abandoning a dependent, but both of them were later found not guilty by a jury.

Natalia's bone test result showed she was at least 14 or above when she was adopted in 2010 and the doctors treating Natalia claimed she was an adult sociopath, according to People.