It is so tempting in closing argument to trash your opponent for not proving their points. But tread lightly, as case law holds that you cannot state or imply fault on a party for failing to call witnesses equally available to both sides. BUT, you can fault them for not introducing evidence. So make your point that way and avoid a mistrial.
In Community Asphalt Corp. and Alfredo Martinez v. Joaquin Bassols, the parties argued over whether the injured plaintiff had missed out on a business deal with the energy drink manufacturer, Red Bull. The plaintiff himself admitted he was unaware he might have even had such a deal which his lawyer had introduced through his sister. In closing, opposing counsel said, “You should expect more evidence than his sister coming into court. You should expect something from Red Bull.”
The Third District (Ramirez, Cope and Salter) concluded that counsel’s remarks permissibly addressed evidence as lacking, not witnesses.