Spiral: From the Book of Saw represents the next stage in the legacy left behind by the Jigsaw killer, as the film showcases through its various traps and the cat-and-mouse chase between the police and the killer. The many nods to earlier entries in the Saw franchise are a great way for fans to be reminded of the past. However, more than the film's other callbacks, the Spiral killer's pig mask outfit reflects the deeper meaning behind his actions.
Spiral eventually reveals the killer is Det. William Schenk (Max Minghella), the partner to the film's protagonist, Det. Zeke Banks. His reason for continuing Jigsaw's gruesome crusade? To take revenge against the corrupt police officers that killed his father in front of him. To do this, he kidnaps them wearing a pig mask, disguising his voice and using the totem of a pig puppet to convey his messages to the police. Not only is his appearance startling and a departure from the Billy puppet from Saw, but it's also his way of mocking the cops.
In society, "pigs" is a demeaning nickname for the police. Although it's not as commonly used as it once was, the pig-related visuals still carry weight in Spiral. Examples include a scene where the killer taunts the police by leaving a pig head in a car that belongs to one of the missing detectives. This idea comes up again when the killer uses their police officer puppet, which has a pig's head, to communicate with Det. Banks. To the police, it comes across as nothing deeper than a copycat killer focusing on the constant pig imagery Jigsaw used. However, it also represents the animosity Schenk has for corrupt police officers.
If his elaborate plan to kill the people tied to his father's killers wasn't enough, Schenk also wants to disrespect them in their last moments of freedom. He is actively mocking the police department and the officers he's targeted by taking them while wearing the mask. Unlike Jigsaw, Schenk doesn't kill to teach anyone a lesson; he only wants revenge and to prove how fragile the justice system is, even at its lowest level. Schenk sees this as the start of a crusade to punish all corrupt cops and treat them like the animals he believes they are.
To Schenk, the pig mask and Jigsaw's mission becomes the perfect alibi. It's a way to make fun of the police and their incompetence and corruption. But it also acts as a way to mask his true motivations by hiding behind the guise of a Jigsaw copycat. However, even deeper than that, it's a visual representation of how Schenk sees the people who killed his father, making them nothing more than animals that need to be eliminated, just as they did his dad.
Spiral is a unique film because it's nothing like its predecessors. While there are traps and ties to Jigsaw, it's actually about revenge and one man's vendetta against the people who took away his family. The pig mask shows that even the simplest concepts can have two meanings. To the viewer, it represents a nod to the past, but its deeper meaning becomes clearer as the film peels back Schenk's many "masks" to reveal the hurt child desperate to find justice for his father by any means necessary.