A South Carolina babysitter was convicted of child abuse this week because a loyal dog alerted the little boy's parents that the woman was mistreating the child, his father and authorities told ABCNews.com

The parents of 7-month-old Finn Jordan suspected something was wrong last year when their dog began to growl and snarl at the babysitter, Alexis Khan, 22.

"We noticed the dog was getting very defensive when Alexis was around. He would growl and stand between her and our son. His hair would stand up on the back of his neck and we knew something was up," Benjamin Jordan said.

Khan had been working with for the family for five months before the Jordans became suspicious. They had run a background check on the woman, who had held previous babysitting jobs, before hiring her to watch the boy while they were at work, Jordan said.

Killian, a black lab and German shepherd mix, was generally a docile and friendly dog and his behavior was out of the ordinary.

Finn's parents placed an iPhone under a living room couch to record audio of Khan, expecting to hear her possibly abusing the dog, according to court documents and officials.

What they heard instead shocked them.

On the recording, Khan can be heard telling the infant to "shut the f*** up" and calling him expletives. The baby is heard crying, and noises that sound like slapping and shaking can be heard.

"We just could not believe it," said Jordan who immediately took the baby to the hospital to be checked out.

Doctors found the boy to be in perfect shape, but alerted the police, according to authorities. Initially, officers worried that an audio recording would not be enough to press charges against Khan, but a Charleston police detective interviewed the woman and got a full confession.

Almost exactly a year to the day that the Jordans first recorded Khan, the woman appeared in a Charleston, S.C., court and pleaded guilty to assault and battery.

The judge sentenced her to the maximum three years in prison and her name will be placed in a registry of child abusers, preventing her from ever again working with children.

"Who knows how many children she has abused or how many more she would have had it not been for our dog," asked Jordan.

Killian is not through being a hero. He is currently training to be a psychiatric service animal.