Various crimes and misdemeanors, including petty larceny, before going to work for the DiMeras (not shown on screen)
Assumed Rafe's identity (January 2011)
Raped Sami Brady while pretending to be Rafe (January - May 2011)
Attempted murder; threw Fay Walker down a flight of stairs (April 2011)
Attempted murder: injected an air bubble into Fay's IV (April 2011)
Murder; smothered Fay with a pillow (April 2011)
Assaulted Sami and Rafe, held them at gun-point (May 2011)
Assaulted Hope Brady (June 2011)
Arnold was a small-time criminal hired by the DiMeras to be part of their revenge plot against Sami and Rafe. Arnold received plastic surgery to look exactly like Rafe Hernandez and tutored on the history of the Brady and Hernandez families. Then when Rafe was hospitalized after a car accident, Stefano switched Rafe for Arnold.
Arnold went home with Sami and assumed the role of her husband. Slowly, he began to unravel Sami and Rafe's marriage by mistreating Sami and her children. Sami believed that the behavior change was because of Rafe's accident.
Arnold would periodically meet with E.J. and Stefano to get further instructions. During one such meeting, Fay Walker overheard the men discussing their scheme. To keep her from talking, Arnold attempted to kill Fay by throwing her down the stairs at the DiMera mansion. When that didn't work, he snuck into the hospital and injected an air bubble into her air bubble. When that attempt also failed, he smothered her with a pillow and killed her.
Nervous that Fay may have known about their plan and told Nicole, E.J. and Stefano paid Arnold for his services and told him to leave town. Stefano gave Arnold a new name and debit card to an account that contained his money. But, Arnold's car broke down on his way out of Salem. While trying to fix it, recent runaways, Ciara and Theo, stumbled onto Arnold. When Bo, who was looking for the children, found Arnold with the kids, Bo assumed that Arnold had found them and thanked Arnold for his good work. Arnold had to return to Salem to fill out paper work. Once home, Sami hoped that this rescue would mean that the real Rafe had returned.
Determined to complete his mission and get out of town, Arnold "accidentally" let Sami overhear a conversation with Dario where Arnold talked about his one-night stand with Alicia. When Sami overheard, she broke up with Arnold again. She grabbed her purse and ran out of the apartment. However, in her rush to gather her belongings, she grabbed Arnold's debit card.
Arnold chased Sami to the Convent of the Holy Cross where he quickly realized that the real Rafe was also staying. Arnold told the nuns that he was looking for his twin brother and learned that Rafe was headed to an apartment complex near by. The apartment complex was the building that housed the safe house. Rafe, Sami, and Arnold all finally came face-to-face. Arnold tried to get Sami to believe that he was the real Rafe by telling her the plan that the DiMeras put into place.
Sami didn't know who to believe until Arnold attacked her. Rafe stepped in to protect her. Rafe attacked Arnold and tied, gagged, and locked Arnold in the bathroom until the two decided what to do with him. Eventually, they moved him to an abandoned warehouse.
Noticing that Rafe was suddenly back in Sami's life, Bo and Hope began to trail Rafe. Their information lead them to the warehouse where the found Arnold. As soon as Bo and Hope figured out that Arnold was an imposter. Bo and Hope teamed up with Sami and Rafe to get proof that the DiMeras created the imposter and thus were responsible for all of his subsequent crimes.
Arnold refused to testify or give any statement against the DiMeras at first. Bo, Hope, and Rafe tricked Arnold into thinking that a fellow inmate, a sultry Colombian mafia princess, would bring him to Colombia with her and her family would protect him. The inmate is actually Rafe's old FBI partner. Arnold agreed to the deal, but before he could give his testimony some of the other inmates mistook him for Rafe and beat him to death.