The first officer has to make sure the crime scene is not damaged, and must keep onlookers and others away from the scene to avoid contamination of evidence. Thus, the first responder can ultimately be responsible for the overall success of the physical evidence gathering and evaluation.
Physical evidence can be anything from fingerprints to ballistic evidence and even footprints and tread prints. Physical evidence can also include weapons and other items left behind at the scene by the suspect. All of this evidence can be used later in trial, but it must be documented and evaluated correctly for it to be effective.
No crime scene is without physical evidence, so understanding how to collect and evaluate it is extremely important for every police officer, no matter their function, because sooner or later, they could be the first responder on a crime scene, and collecting or managing physical evidence could fall on their shoulders.
Editors. “Crime Scene Response and Physical Evidence.” SCCJA.org. 2007. 20 Nov. 2007. http://www.sccja.org/csr.htm
OConnor, Thomas. “An Introduction to Criminalistics and Physical Evidence.” Austin Peay State University. 2007. 20 Nov. 2007. http://faculty.ncwc.edu/TOCONNOR/315/315lect02.htm.