Tom gathered the evidence that Gatsby is a bootlegger.
Step-by-step explanation:
Gatsby hated to work as a janitor which was the source of income to pay off his tuition fee. He felt it was humiliating and degrading. When he met Dan Cody and traveled with him, he was instantly moved by the sight of luxury and wealth. Cody left $25,000 for Gatsby after his death but Gatsby was never able to claim it because of Cody's mistress. This made Gatsby earn a remarkable wealth of his own.
Gatsby made most of his money by buying several drugstores on roadside. He also earned some by selling grain alcohol, which was strictly illegal in that era of time, over the counter. These ventures brought a lot of money to Gatsby. When Tom revealed this in front of Daisy, the trust and confidence she had in Gatsby was destroyed.