In Fitzgerald's The Great Gatsby, how does Tom sense immediately that Gatsby is a bootlegger?

Tom is skeptical about Gatsby from the moment he meets him. He first learns that Gatsby and Daisy already know each other. He says: 

I wonder where in the devil he met Daisy. By God, I may be old-fashioned in my ideas, but women run around too much these days to suit me. They meet all kinds of crazy fish. 

Tom doesn't trust Gatsby and he doesn't like Daisy going to parties by herself. As a result, he goes with Daisy to Gatsby's next party in Chapter 6. At the party, Tom is unable to get any information about who Gatsby is or how he has so much money. Then he assumes Gatsby is a bootlegger to account for Gatsby's money. When Nick asks Tom where he'd heard that Gatsby is a bootlegger, Tom says, "I didn’t hear it. I imagined it. A lot of these newly rich people are just big bootleggers, you know." In the next chapter, Tom reveals to Nick and Jordan that he has been investigating Gatsby's past. When Daisy scolds Tom for interrogating Gatsby, Tom says, "‘I suppose the latest thing is to sit back and let Mr. Nobody from Nowhere make love to your wife." 

Although Tom is judgmental in general, he is somewhat justified in being skeptical. Other than Nick, no one really knows Gatsby's past or how he has wealth. Tom assumes the worst.