News of Pinato’s death comes after a petition calling for his return had gathered more than 30,000 signatures by Friday afternoon.
On Thursday, Mr. Longo said he was raising money for legal fees against the DEC. A GoFundMe he set up has raised around $13,500 (£10,400).
The ordeal, he said in a morning message on Friday, had been a “horrible nightmare”.
After Peanut’s death, Mr. Longo posted DEC’s phone number online and urged supporters to call the organization to “express their feelings.”
“We will not let this be the last memory of Pnut,” he wrote.
In a separate Instagram story, he thanked Peanut fans for the “love and support” his family has received and called for donations to help other animals kept at his “freedom farm.”
In a statement, the DEC said the investigation was launched after receiving “numerous reports from the public about the potentially dangerous housing of wild animals that may carry rabies and the illegal keeping of wild animals as pets.”
Mr. Longo took in Peanut seven years ago after spotting his mother’s baby squirrel that had been hit by a car.
He cared for Pinato until he was strong enough to be released, but said the next morning he found the creature on his porch with “a piece of its tail missing.”
In that time, Peanut’s Instagram account has amassed over 500,000 followers.
The account features videos of Peanut acting out skits with Mr. Longo, occasionally wearing a hat, often climbing over or hugging him, and regularly eating waffles.