The Princeton, New Jersey, man accused of killing his brother and a family cat allegedly told police he had a "fit of madness" when they responded to the scene of the crime.

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

Officers also found a bloody knife, fork and plate near victim Joseph Hertgen’s body, the source said — which has led cops to believe accused killer Matthew Hertgen, 31, consumed the missing

More gruesome details have emerged in the case of Matthew Hertgen, a former college soccer player who brutally killed his younger brother and their family cat.

It was gruesome. It was way overboard, he even killed the cat, setting him on fire,” said a cop source at the scene.