Girolami also handed Peterson’s defense a procedural victory by scheduling a preliminary hearing for July 16 at which prosecutors will attempt to show that there is sufficient evidence to try him on murder charges.Summer CircusA preliminary hearing gives defense attorneys the opportunity to cross-examine any witnesses the prosecution calls and to challenge evidence. The public hearing is an alternative to the impaneling of a criminal grand jury to consider whether a trial is justified, a secret proceeding in which the defense plays no role.