A probable cause affidavit sheds more light on the arrest of Matthew Hertgen, who is accused of murdering his brother and a cat in grisly fashion -- as police detail the scene, body and why his other brother was concerned about Matthew's behavior before the incident.

A New Jersey man was in a “fit of madness” and experiencing “terrifying visions” when he allegedly murdered his younger brother, according to new details from the Mercer County Prosecutor’s Office.

Matthew Hertgen said he fell into a “fit of madness” the night his brother’s beaten body and the burnt remains their cat were found inside an apartment near Princeton University.

Matthew Hertgen is accused of brutally killing his brother, Joseph Hertgen, in Princeton. A relative told police he has struggled with terrifying visions.

A detective’s affidavit described a gruesome scene when Princeton patrol officers arrived at the brothers’ apartment on the night of the killing.

Matthew Hertgen may have been been suffering from severe mental illness for years before the alleged murder A plate and utensils smeared with blood were allegedly found inside the home of a Princeton,