According to the criminal indictment, "a photo of a cat lying motionless in a pool of what appeared to be blood was posted on Instagram" by David Mosley.
The post circulated social media, prompting outrage across the animal activist community.
The court document reveals new details in the investigation.
It noted that police "observed dried biological material" inside Mosley's home. The ASPCA identified it as feline blood.
Mosley is being charged with criminal mischief and animal cruelty.
On Tuesday, Mosley appeared in front of a packed courtroom. Protesters were seen outside of the courthouse chanting and holding signs.
He pleaded not guilty to both charges.
"We were leaning forward physically on the edge of our seats, waiting for the verdict of guilty," said animal activist Carter. "And when we heard not guilty, I recoiled in anger and horror, in frustration and disappointment."
Protestors were left unsatisfied.
"I would like to see him in jail, and I would like him to get the treatment that he needs because he's obviously not right in the head," said animal rights activist Rachel Ejsmont.
Activists said they will continue to show up until justice is served.
Mosley is due back in court on March 17.