Obsession.

James M. Dougherty was an industrious young man in Brooklyn in the 1880s. He worked as a lineman for the Postal Telegraph Company and in his spare time he studied meteorology, electricity, astronomy and other sciences. He dabbled in a little of everything until after watching a play he became obsessed with the leading lady, Mary Anderson, and his love for her became his sole controlling passion.

Dougherty began to follow Mary Anderson wherever she performed. His obsession with the actress led him to believe that an organized conspiracy of his enemies worked to keep them apart. When Dougherty's stalking came to the attention of the police, he was declared insane and sent to an asylum.

He escaped from the asylum, but returned with a revolver and murdered the superintendent. 

“I am not crazy,” said Dougherty after his recapture, “but as sane as the sanest man that walks New York today.”

Read the full story here: Lunatic Dougherty.