Perhaps conscience is an artificial construct, and none of us have it. Or maybe, some criminals are criminals because that is the only thing They can conscientiously do, like a mother who steals food for her children.
Socrates believed the voice in his head a gift from the gods; an inner daemon making him unique. More likely, we all have an ongoing discussion in our head, each of us debating the right thing to do. Cool calculation may reveal it profitable to disregard the winner of this debate. After repeatedly disregarding this inner voice, and possibly profiting, the weaker voice may appear as the stronger. That's called "losing your compass".
Personally, I believe being atheist means assuming a larger responsibility for those decisions of conscience. After all, the atheist can no longer rely on scripture or that booming voice from the sky to step in and lead the way. This complicates our lives in some ways yet simplifies it in others. I'm not led by simple instructions from elsewhere but I am more empathetic and have worked to better understand my place in society.
Maybe this is why crime goes down during economically prosperous times. The calculations result in different results. Of course, if the compass is completely lost, the calculations are rigged.
It's like in cricket.
Does a fast bowler deliberately aiming the ball at the batsmans couilles [french coloq.] have a conscience ? Or, should we ask the question, what for ?