Paranthetical to my previous post.
One reason for caution in interpreting the data is explained here.
Though I do remember a survey being conducted on prisoners before they entered the prison system, and again from memory it had a disproportionately low percentage of atheists.
Either way there is no data I’m aware of that indicates atheists are les moral per se than theists. Though to be objective it would have to compare them under the same circumstances obviously.