Although it is beyond the scope of this document to analyze court decisions or cite precedents, fundamental issues related to the admissibility of demonstrative evidence are useful to discuss.

Recent court decisions have given trial judges discretion regarding issues related to demonstrative evidence admissibility. Paying attention to the fundamentals will greatly reduce the chance of any problems. The most fundamental concern for probative demonstrative evidence is foundation. Just as an expert has to have a legitimate, scientific basis for his opinions, the demonstrative evidence needs to be developed based upon and be consistent with these opinions. The demonstrative evidence developer has no opinion, and bases all of his work on the work of the testifying expert. The expert or developer needs to be able to provide the data to prove this. The demonstrative evidence developer needs to be chosen as carefully as the expert to make sure they understand these issues and can accurately create the demonstrative evidence to represent the expert’s testimony.

Note that non-probative demonstrative evidence, sometimes referred to as illustrative evidence, does not have the same burdens of admissibility as demonstrative evidence used as part of the proof of the case, but it still must be accurate and useful. For instance, portrayals of vehicle dynamics must follow the laws of physics. Fact witnesses may need to testify to the accuracy of a portrayal. For example, the husband of the deceased may testify that the “Day In The Life” portrayal of his wife is factual.  All demonstrative evidence must assist the trier of fact. If the demonstrative evidence does not contribute to the process at hand, it may be excluded.