What do these numbers mean? There are a few possibilities. Differences among the justice could reflect an unthinking bias either in favor of or against criminal defendants. They could reflect a willingness on the part of some justices to take heed of public opinion which, conventional wisdom holds, is hostile to (and undervalues) the rights of criminal defendants.
Those explanations are possible but I think they are wrong. My own view is that these differences reflect different philosophical bents. Justices who rule more frequently for criminal defendants may be more skeptical of law enforcement. They may balance the tension between public safety and the desire to avoid wrongful convictions differently than justices who are less likely to rule in this way. They may adopt interpretive techniques that privilege the claims of the accused or that are more likely to credit claims made by groups such as the Wisconsin Innocence Project.
There is more to these differences than whether they result in more or fewer rulings in favor of criminal defendants. But we can't begin that discussion without acknowledging that there are differences. To suggest that, in deciding these cases, justices are just mechanically applying the law or that there is no difference between judges on these questions (no "liberals" and "no conservatives" if those are the terms that we want to use) is just wrong.
There are big differences and the public is entitled to know that. To deny what every lawyer in the state knows to be true, i.e., Louis Butler is significantly more liberal on criminal justice issues than other justices such as Prosser, Roggensack and, prior to his retirement, Wilcox, is a deception.