What should an investigating officer do first after taping off a crime scene?

The first thing an investigating officer should do upon arriving at a crime scene is to secure the crime scene. Failure to secure the crime scene could cause all sorts of problems if the case ends up in court. If the crime scene isn’t secured, evidence could be removed or altered. If the evidence is tampered with because the crime scene wasn’t secured, charges could be thrown out in a court case because the judge could not be sure if the evidence presented in the case is the actual evidence from the crime scene. A good defense attorney would use the failure to secure a crime scene to the defendant's advantage when presenting the case. Of course, a good police officer would also know securing the crime scene as soon as possible is of utmost importance.