Here is one of the worst cases of prosecutorial misconduct ever, straight from my Wrongful Convictions class...
http://www.pbs.org/wgbh/pages/frontl...ws/case/cases/
Read the one on Roy Criner and read some of the statements from the DA in that case.
Here's another doozy...
http://www.pbs.org/wgbh/pages/frontl.../robinson.html