It all comes down to the day of August 4th, 1892, much about the case is obscure but what we do know is that around 11 o'clock on that thursday, Lizzie Borden yelled upstairs to the maid "Come quick!, Fathers dead!", soon the body of Abby Borden Lizzies stepmother would be found also upstairs, she was killed knelt down presumably while making the bed. For a while the maid, and Lizzies uncle John were prime suspects. No one would believe someone as quiet as Lizzie was capable of such attrocities.
The maid was outside cleaning the windows at the time of the murders, and the Uncle had an alliby of his whereabouts. There was no evidence to suggest that an outsider was responsible. The crimes were no where near clean, a hatchet style axe had been used first on the stepmother, and then on the father. Lizzie Borden despised her stepmother with all her soul, from her early teens after some personal family tiff she would no longer call her mother and from then on right up to her 20's addressed her by her first name.
Lizzie loved her father however, and was battleing two inner struggles, one the man whom she loved as a father was wed to the person she hated the most in the world and whenever he financially secured his wife it did nothing but make her seethe with anger. The second battle within was maybe the second reason she butchered the couple. Lizzie was known to have epileptic fits, however during these fits she would black out and not always collapse and convulse but rather act things out, generally violently. This is a well believed theory.
People question, if she loved her father then why kill him. First of all he didn't recieve half as many blows as the mutilated Stepmother which was definately a crime of passion. And secondly if he had discovered the body, he would know that Lizzie was responsible and would never love her again, also it would break his heart so instead she "freed" him of that pain.
Though she was found not guilty the public shunned her and she led a very isolated life from there on.