Zoosadism

Zoosadism is sexual pleasure derived from cruelty to animals. It is a paraphilia, where people are sexually aroused by torturing animals. Zoosadism is part of the Macdonald triad, a set of three behaviors that are considered a precursor to psychopathic behavior.

Research
Some studies have suggested that individuals who are cruel to animals are more likely to be violent to humans. According to The New York Times:

The FBI has found that a history of cruelty to animals is one of the traits that regularly appear in its computer records of serial rapists and murderers, and the standard diagnostic and treatment manual for psychiatric and emotional disorders lists cruelty to animals as a diagnostic criterion for conduct disorders.

Helen Gavin wrote however in Criminological and Forensic Psychology (2013):

This is not a universal trait, though. Dennis Nilsen had difficulty initiating social contact with people, but loved his faithful companion, Bleep, a mongrel bitch. After his arrest, he was very concerned for her welfare, as she was taken to the police station too.

Alan R. Felthous reported in his paper "Aggression Against Cats, Dogs, and People" (1980):

A survey of psychiatric patients who had repeatedly tortured dogs and cats found all of them had high levels of aggression toward people as well, including one patient who had murdered a boy.

This is a commonly reported finding, and for this reason, cruelty to animals is often considered a warning sign of potential violence towards humans.

2018 zoosadist scandal
In September 2018, a whistleblower tweeted a link to a Telegram channel.

“Zoosadist Evidence” was the name of the channel which contained images, video, and discussion of extreme violence to animals, and the whistleblower alleged that the members involved were specific individuals in the furry fandom.

One zoosadist exposed during the 2018 zoosadism scandal was an adult member of the furry fandom in Cuba, by the name of Rubén Marrero Pernas, or simply known as “Woof”. Pernas was found to be raping, torturing then killing dogs and puppies and recording the acts online for a group of zoosadists on Telegram who found this to be sexually gratifying. Pernas being exposed lead to public outrage, and eventual legal reform.

Even years later, the effects of this are still evolving, most notably with the 2022 arrest and the 2023 guilty plea of notorious Telegram zoosadist Adam Britton.

Other examples
Serial killers such as Ted Bundy and Jeffrey Dahmer were known for torturing and killing animals in their youth.

A Canadian man, Leighton Labute, was arrested in 2020 for torturing and killing three hamsters, and uploading the video to social media.

In June 2023, the BBC uncovered a global monkey torture ring, where participants would produce and distribute videos of monkeys being hurt and killed.

Legal status
In 1999, the United States Congress enacted a statute affecting the legality of crush films which criminalized the creation, sale, and possession of depictions of animal cruelty, though with an exception for "any depiction that has serious religious, political, scientific, educational, journalistic, historical, or artistic value."

In 2008, the United States Court of Appeals for the Third Circuit invalidated the ban on the sale and possession of such films (if not otherwise obscene) as a violation of the Constitution's guarantee for freedom of speech. The United States Supreme Court affirmed the Third Circuit's decision in United States v. Stevens, finding the law unconstitutional because the law was so broad and vague that it included any portrayal of an animal in or being harmed such as by hunting or disease.

On November 28, 2010, bill H.R. 5566, which prohibits interstate commerce in animal crush films, was passed by the House of Representatives and the Senate, and on December 9, the bill was signed by President Obama becoming the Animal Crush Video Prohibition Act of 2010.

On September 8, 2015, a Houston woman pleaded guilty in the nation's first federal animal crush video case.

On November 25, 2019, President Donald Trump signed into law the PACT ACT, the Preventing Animal Cruelty and Torture (PACT) Act, which authorized the FBI and other federal law enforcement agencies to prosecute malicious animal cruelty. The PACT act defines animal crushing as when "one or more living non-human mammals, birds, reptiles or amphibians is purposely crushed, burned, drowned, suffocated, impaled or otherwise subjected to serious bodily injury."

Criticism of alleged link to violence against humans
On the other hand, Piers Beirne, a professor of criminology at the University of Southern Maine, has criticized existing studies for ignoring socially accepted practices of violence against animals, such as animal slaughter and vivisection, that might be linked to violence against humans.