Apolice officer is at a crime scene and locates a footprint in a flowerbed near an open window. the window is examined closely and pry marks are discovered on the lower window sash and the window sill indicating forced entry. the police officer pointed out the evidence to the investigator who photographed the evidence and collected the footwear impression using a liquid footwear casting system. who is required to testify in court to get the evidence admitted during the trial?