HUMAN SOURCES OF ERRORS TRIALS BASES.

CHAIN OF CUSTODY: There are many sources of error. Evidence has to be discovered (police or criminalist), it has to be collected (police, crime scene technician, or criminalist), and then it has to be packaged, labeled, and transported (police supervisor or criminalist). Once it gets to the lab, it has to be logged in, assigned an identification number, placed in storage, kept from intermingling with other evidence, and analyzed (criminalist, crime lab technician, or forensic scientist). 

THIS CHAIN OF

• Testimonial -- this is the kind of evidence that comes to court through witnesses speaking under oath or affirmation. They could be testifying about something they saw (eyewitnesses), something they heard (hearsay witnesses), or something they know (character, habit, or custom witnesses)
• Physical -- these are tangible objects that are real (sometimes said to speak for themselves because they can be taken into the jury room), direct (no preliminary facts needed), and not circumstantial (do not require an inference to be made), although circumstantial evidence is sometimes offered and strengthened by expert testimony. Examples of physical evidence would include the gun used to commit the crime, trace particles found at the crime scene, property recovered, fingerprints, shoeprints, handwriting, etc.
• Documentary -- this is usually any kind of writing, sound or video recording. It may be the transcript of a telephone intercept. Authentication of the evidence is usually required along with expert testimony at times.
• Demonstrative -- these are types of real evidence used to illustrate, demonstrate, or recreate a tangible thing; for example, a cardboard model mockup of the crime scene or other constructed-to-scale models. The purpose of this stuff to to replace timely, expensive, and possibly prejudicial jury trips to the crime scene.

    Both forensic scientists and criminalists need to be intimately familiar with the Standards of Admissibility for Scientific Expertise, since these  CUSTODY HAS TO BE PERFECT EFFICIENT AND CLEAN /THIS IS THE WORD SO ...