American prosecutors have learned that conviction rates generally go up when additional charges and defendants are added to criminal cases.
Consequently, state and federal prosecutors routinely stack indictments with multiple (repetitive) counts so that juries will be more likely to convict defendants.
A study of thousands of criminal cases found that when a defendant is charged with one count, he has a 66 percent chance of being convicted; but when he is charged with three or more counts, the conviction rate goes up to 78 percent.
And when a defendant faces three or more counts, he has an 88 percent chance of being convicted of Count 1 (which is generally the most serious count).
See this detailed law review article by Andrew D. Leipold, “How the Pretrial Process Contributes to Wrongful Convictions.”
See also my own discussion on the explosion of multi-count indictments.