Reviewing federal cases, USA Today found 201 instances of prosecutorial misconduct confirmed by federal courts (in about a ten year period). In a study of the California justice system, the Northern California Innocence Project found over 700 cases (during a 10 year period) in which "courts explicitly found that prosecutors committed misconduct." Usually they get away with it (and some are repeat offenders), according to the Innocence Project report: The California state bar disciplined only a tiny fraction of prosecutors found by courts to have engaged in misconduct.
The prevalence of wrongful convictions, resulting from a range of systemic inequities including misconduct, isn't news to defense attorneys and shouldn't be news to the public, given widely publicized cases involving the post conviction exonerations of people who've been wrongly imprisoned and in some cases sentenced to die. (According to the Innocence Project, 17 people exonerated by DNA evidence had received death sentences; on average, exonerees served 13 year prison sentences before being released.)
Exposing abuses in the administration of the death penalty has helped deter its practice: In Illinois, which declared a moratorium on capital punishment in 2000, the legislature has voted to repeal the state's death penalty. Even in Texas, the number of death sentences has declined. (Texas probably executed an innocent man in 2004, as David Grann famously demonstrated in The New Yorker.) But in less dramatic cases, including those involving lengthy, wrongful imprisonments, prosecutorial misconduct is often tolerated, if not trivialized, as its persistence shows. The wrongful imprisonment of innocent people and ruination of innocent lives resulting from intentional government misconduct simply does not arouse the outrage and demands for reform that follow a fateful parole decision, resulting from unintentional mistakes.
In fact, the call for harsher penal laws sparked by a mistaken grant of parole can exacerbate the problem of misconduct by increasing the generally unaccountable, discretionary power of prosecutors through mandatory sentencing schemes, which (as I've noted here) effectively consolidate charging and sentencing authority in the prosecutor's office. In Massachusetts, police and some legislators are pressing for passage of an emotionally charged law (named for murder victim, Melissa Gosule) that would impose mandatory maximum penalties on many third time felony offenders, eliminating opportunities for parole.
But three strikes laws, popularized in the 1990s, are more reliably effective in increasing prison overcrowding than reducing violent crime (outside prison), and in an apparent effort to stave off passage of "Melissa's Law," Governor Patrick has proposed a compromise bill that would increase sentences for some repeat felons and limit but not abolish parole for them: Most offenders will be released eventually if only for a lack of resources to imprison all of them forever. Parole provides at least hope of supervising and easing their re-entry. Patrick calls his proposal a more "sensible," and smarter approach to crime control, although it may be less sensible than no proposal to increase already stiff sentences for felonies and impose new limits on parole, which parole board members will be more fearful of granting anyway, after the Cinelli fiasco. And, the Governor's bill obviously lacks the visceral appeal of a harsher law named for a young female homicide victim.