The Fall of the House of Usher: Why did Madeline and Roderick tie Griswold to some pipes and wall him in?

In the final episode of The Fall of the House of Usher, titled "The Raven," it is revealed why Madeline and Roderick tied Griswold to some pipes and walled him in. The episode provides insight into the events that led to the destruction of the Usher family and exposes their rise to power through murder and deals with supernatural entities.During a New Year's Eve party, Madeline proposes a toast to celebrate Roderick's victory over Aguste Dupin and the government. Unbeknownst to Griswold, Madeline laces his drink with cyanide. Afterward, she seduces him and leads him to the basement, where the construction of the Fortunato building is happening. The workers have been dismissed, providing the perfect opportunity for Madeline and Roderick to dispose of Griswold discreetly. They tie him to some pipes and wall him in, leaving him alive to suffer for a week until he ultimately dies.Following this gruesome act, Madeline and Roderick need an alibi to distance themselves from the crime. They end up at Verna's bar, where they are presented with a deal they can't refuse. Verna, a woman seemingly connected to death itself, offers them everything they desire in exchange for the end of their bloodline. With a toast and a bottle of cognac, they accept the deal, oblivious to its consequences. As they leave the bar, it disappears, and they forget the encounter until death comes for them.In the midst of these events, Lenore, one of the Usher children, provides a truthful statement to the police about her father's abuse of her mother. She sends Morelle off for treatment and grants her a chance at a long life dedicated to helping others. Lenore then meets with Verna in her grandfather's guest bedroom, where Verna, with a tap of her finger, swiftly and painlessly takes Lenore's life.While all of this unfolds, Madeline activates an AI version of Lenore based on her social media posts. However, the AI malfunctions and incessantly sends Roderick the message "Nevermore," reminiscent of Edgar Allan Poe's poem "The Raven."As Madeline starts to question her fate, she seeks an escape, prompting Roderick to ensure she fulfills her end of the deal. He poisons and embalms her, mimicking the ancient Egyptian process. But Madeline, filled with rage, rises from her sarcophagus and chokes Roderick to death in front of Auguste. This mirrors Eliza's murder of Mr. Longfellow in the show's initial episode and signifies the end of the Usher dynasty.With the Usher family gone, the epilogue reveals the aftermath. Juno inherits Fortunato Pharmaceutical, dissolving the company to start a foundation aiding those struggling with addiction. Arthur Pym becomes the only one arrested by the government due to evidence collected by Camille. Auguste retires and lives a peaceful life, leaving a tape recorder at Roderick's grave containing their conversation. Verna, taking the form of a raven, returns mementos to each victim as a reminder of their lives and deaths. Lenore receives a feather and a white rose as a tribute to a life well-lived.In conclusion, the reasons behind Madeline and Roderick's decision to tie Griswold to pipes and wall him in were a culmination of their desire to eliminate a potential threat and preserve their reputations. They resorted to extreme measures to dispose of him discreetly, ultimately sealing their fate as the Usher family's destructive legacy unfolded.