They had done many illegal or bad things in the past. In the beginning, they were scared of being caught or regretted what they had done. After getting financial benefits from those things, they threw their consciences into the ocean.
Making money daily without hard work from 9 a.m. to 5 p.m. was their dream. Once they tasted the sweetness, they became more and more fearless. After they had committed three crimes, they couldn't stop. It was like they were drug addicts.
Karl Marx once said that people would take a risk if they could make a 50% profit out of capitalism. They would become heartless oppressed creatures if they could make a 100% profit.
These men didn't need to invest anything into their business to make double or even triple profits. They formed their own gang and had their own rules and regulations.