This paper is an analysis both of the presentation formats and sample types most frequently used in court case simulations, and of the strength of the evidence given in a trial, which are relevant factors for the verdicts returned by jurors. The samples selected have been taken from citizens eligible as jurors according to Spanish law. Real cases of manslaughter have been used. The results obtained show that the type of sample, the presentation format and the strength of evidence have an independent effect on the jurors' decisions. The strongest influence on verdict is attributable, first, to the evidence; secondly, to the type of sample; and, finally, to the presentation format. The effects caused by the studied variables on the jurors' verdict tendency also seem to recur in some of the relevant questions which make them explain and justify their verdicts, the effect being more noticeable with ambiguous evidence.