Firstly the dictionary definition of the word Forensic:
Therefore, Forensic Science is the application of a science to criminal and civil laws during an investigation, as governed by the legal standards of admissible evidence and criminal procedure.
Collision Investigators attend scenes, collect, and analyse evidence and use scientific methods and techniques to investigate the cause of that collision. Thereafter, they present their evidence in a written and/or oral format for the benefit of a court of law [or other hearing]. In this respect a collision investigator is a forensic scientist.
Having been provided with or gathered the relevant information, the collision investigator then has to decide which examinations or tests are appropriate and relevant to the case or dispute. Then they must conduct the most appropriate tests and/or analysis and document the process. They then must interpret the results and write a clear, concise, report documenting the steps followed to reach their conclusions or opinions.
The collision investigator will, at some point, have to testify, under oath, to the judge or jury. They are expert witnesses as opposed to ordinary witnesses and as such are permitted to testify not just about what the results of testing or analysis were, i.e. facts, but also to give an opinion about what those results mean.
The work of the collision investigator is intended to be used in court and because their evidence can be very powerful, they must be accurate, methodical, detailed and remembering their role is for and on behalf of the court - unbiased.
A party to a court case may challenge whether the expert is properly qualified to render an expert opinion or question the scientist’s impartiality so remember the words of Dr Brouardel, a 19th century French pathologist:
“If the law has made you a witness, remain a man of science. You have no victim to avenge, no guilty or innocent person to convict or save — you must bear testimony within the limits of science.”
Irrespective of who instructs or pays the collision investigator's fees, they are in court to assist the court and no one else.