Saturday night, George Zimmerman was acquitted of all charges relating to his killing of Trayvon Martin last year. That's a pretty improbable outcome for a murder trial. According to the Bureau of Justice Statistics, in 2006, 81 percent of murder defendants were convicted: 42 percent due to a plea, 39 percent after a trial. Just 5 percent of cases ended with an acquittal at trial. Other than driving offenses, murder has the highest conviction rate of just about any felony:
So how did Zimmerman get off? Maybe it's just that publicity makes convictions less likely. Between Robert Blake, Casey Anthony and, of course, O.J. Simpson, it isn't hard to think of high-profile murder defendants who beat the odds and got acquitted. Do juries have a weakness for the famous and accused?
There is extensive research literature on what social scientists call "pretrial publicity" or PTP. Many studies rely on an experimental design in a laboratory setting, where participants — typically college students, or potential jurors in the community where the research is being conducted — are exposed to different types and amounts of media coverage about either real or fictional cases, and then asked about their feelings toward the defendant.
Most of the research along these lines finds significant effects, most of which suggest that exposure to facts about the defendant or the crime can bias would-be jurors against him or her. "Media coverage containing case-specific information, inadmissible information, and emotional accounts of trials has the potential to influence jurors’ perceptions of defendant culpability, which may lead to a significantly greater chance that a defendant is ultimately found guilty," write Lisa Spano, Jennifer Groscup and Steven Penrod in their summary of the research. Survey evidence about real trials actually shows stronger effects than do experiments.
So that would seem to suggest that publicity leaves high-profile defendants worse off. But more recent research has looked at "positive PTP," or pro-defendant coverage, which has a similar but opposite impact. In 2011, Christine Ruva, Christina Guenther and Angela Yarbrough at the University of South Florida found that positive PTP significantly increased experiment participants' likelihood of concluding the defendant was not guilty. A 2012 paper by Ruva, Jessica Mayes, Mary Dickman and Cathy McEvoy found the same. Interestingly, it also found that alternating exposure to positive and negative coverage had the net effect of making study participants more likely to favor the defendant. "The point-counterpoint presentation resulted in a pro-defendant (or pro-acquittal) bias," the authors conclude.
The research seems to suggest that unambiguously anti-Zimmerman press coverage (similar to the very anti-Casey Anthony or anti-Scott Peterson coverage that preceded those trials) would have prejudiced jurors against him and that split or pro-Zimmerman coverage would have helped him out. So what kind of coverage did Zimmerman receive?
Polling is an imperfect proxy for the nature of news coverage, but it suggests that the public is generally divided on Zimmerman's case. A Rasmussen poll from May found that 31 percent of Americans wanted him convicted of murder, 29 percent thought he was acting in self-defense, and 40 percent were unsure. That's a slightly worse result for Zimmerman than polls a year previously, but better for him than public opinion in March or April 2012. A Pew Research Center survey found that Democrats and blacks were more likely to follow the case, and that MSNBC and CNN provided much more airtime to it than did Fox News. That suggests that media coverage was likelier to come from a more Zimmerman-skeptical outfit (MSNBC) than one likely to doubt the case against him (Fox News). But CNN, which doesn't have a clear ideological stance, also covered the case and subsequent trial aggressively.
We'll never know for sure how the media's coverage of the case influenced its outcome. But given Ruva et al's finding that mixed coverage tends to help the defendant, it may be that the media's not purely pro-Zimmerman, not purely anti-Zimmerman coverage ultimately redounded to his benefit.