Police have now tracked down the person they say put it there.
Officials say 28-year-old Steven Elias is the man behind the disturbing act, which was captured on surveillance video.
The video footage captured a person walking onto the Saladino family's Cranford property on the night March 12 with an object in hand.
New Jersey homeowner finds dead cat inside her mailbox
After a nearly three-month long investigation, authorities identified Elias as the person behind it.
Elias was charged with several offenses related to the disturbing crime, including third-degree causing fear of unlawful bodily violence, harassment, and criminal trespass for placing the deceased cat inside the mailbox.
Authorities say the cat appeared to have been hit by a car or killed by another animal.
Elias was issued a summons.