Radley Balko complains that "prosecutors are almost never sanctioned for misconduct, even egregious violations that lead to wrongful convictions." It's a subject he covered at length in a recent column. A study of prosecutors in California bolsters his case:
The Northern California Innocence Project reviewed 4,000 cases between 1997 and 2009 and found prosecutorial misconduct in 707 of them (though they caution that this may underestimate the problem). In only six of those cases were prosecutors sanctioned by the California Bar.