Dorothea Puente was "considered a Mother Theresa."

However, the elderly woman is the culprit of the nine confirmed murders.

In the eighties, Puente ran a boarding house ins Sacramento, California, where she would onboard elderly and disabled persons before murdering them and cashing in their social security checks.

John Cabrera, the detective on the case, gave an exclusive first look at the story.

"'Murders at the Boarding House' refers to what she was running. I had nothing to indicate that these murders had gone on in her house. She was very, very skilled in what she was doing, and that's why she was able to get away with this for two years," Cabrera said.

The detective knew that she'd be a tough case to pursue, but knew it was the right thing to do.

"I was gonna work this case, because I just felt [that there] was something in the air that I needed to find out. I want people to know who she really was. Deep down I knew there was something more sinister."

Murders at the Boarding House premieres April 17th on Oxygen.