In a state governed by law, no person may be convicted unless he or she is found guilty. The objective of the Police is to serve the state and protect the citizens by preventing and investigating crimes.

The “S-rule” describes the goal of police investigation:

Search, secure, collect CLUES (Søke, sikre, samle SPOR) that may substantiate the case, the accused’s guilt as well as their innocence.

What happened, where when and how?
Who was involved?

The police collect pieces of a puzzle and try to put the pieces together to form a picture that will show the court what probably has happened on a scene of a crime. The tactical investigators collect information and interrogate witnesses. The technical investigators are intended “to interrogate the silent witnesses”, that is to interpret the physical clues on the scene of a crime. What may a fingerprint, a footprint or a strand of hair tell us?

Witnesses may forget, misunderstand, and even lie, but we say that the silent witnesses never lie.
Or is it that simple?

Station 1: What is a clue?

“All contact leaves a clue”
– Edmond Locard (b. 1877), French forensic technical pioneer

The body leaves clues all over the place. Prints are made on all surfaces. Microscopical drops of sweat and saliva are left when you talk or move around. Fibres, dust, and pollen sift from clothing, and the body will leave skin cells and hair. We leave odours that a tracker dog may follow. Footwear, vehicles, tools, and weapons leave physical clues, and a lot of the technology we depend upon in our daily lives, store digital clues.

Everything that may exclude or link a person to a crime scene on the time the crime was committed may constitute relevant clues in an investigation and may be presented as evidence in a court case. One individual piece of evidence seldom constitutes the basis for conviction. In the court, the question of guilt is assessed on the basis of all the evidence. All the minor and major clues that indicate guilt or innocence are to be balanced against each other.

Station 2: Analysing the clues

When the clues have been secured and collected, they are analysed. Some clues are best analysed on the crime scene, whereas others are brought to the laboratory. The clues are studied under microscope, photographed, and undergo chemical or technical tests.

Modern methods of analysis have their basis in scientific methods developed in the Age of Enlightenment in the 18^th and 19^th centuries. In 1901, blood types were identified for the first time. Only one year after, the discovery was used to solve a murder case in Germany.

During the 20^th century, the development within forensic technique took speed. In 1931, the Forensic Laboratory in Oslo was established with equipment for technical and chemical methods of analysis. The laboratory expanded as time went on and was named Kriminalpolitisentralen – Kripos.

Kripos assists the police in the investigation of crimes and accidents all over the country. Lots of the work requires special competence. More and more precise tools make it possible to analyse new types of clues or make new and more precise analyses of old clues. Currently, around half the employees at Kripos are civilian experts such as chemists, photographers, IT experts and experts in detecting forgery.

Station 3: The silent witnesses speak

The forensic technicians give the silent witnesses a voice. The clue itself cannot say anything before people interpret it. After the chemical and technical analyses have been completed, the results must be interpreted. Some clues may seem unambiguous, whereas the interpretation of others may be discussed at great length. Even a “secure clue” such as DNA, has its limitations. It is, for example impossible to say when the clue was left on a crime scene.

The interpretation of a clue must be made on a scientific basis, and the analysis of all clues therefore follows the scientific development. Current methods of analysis produce increasingly more certain results, but the conception of what is a secure clue has changed.

The forensic technicians’ conclusions are presented in a report that is presented in court. In addition, experts testify and explain complicated clues. The Norwegian courts of law have free evaluation of evidence. This means that the court itself must assess the importance a piece of evidence is to have in a particular case. Some clues may indicate that the suspect is guilty, others that he is innocent, and the court decides what is to be emphasized.

Station 4: Miscarriage of Justice

In a state governed by law, you are innocent until the opposite is proven, and the doubt should always be to the benefit of the accused.

If the police tie itself to one hypothesis too early in the investigation, they risk being prone to confirmation bias. In such cases, one may easily overlook clues that do not confirm the hypothesis. The investigators look for pieces in a puzzle. If they, in advance, decide what type of picture they expect to see in the end, they risk looking for only such pieces that fit in, and discard those that do not fit in.

The police, the prosecution authorities and the court have a duty to be objective throughout the legal process. They must be open, question the evidence and look for alternative explanations. The standard of proof in Norwegian criminal law is quite strict. The court must be convinced about guilt beyond any reasonable and sensible doubt in order to sentence anyone. Nevertheless, legal errors occur that lead to the convictions of innocent people for crimes that they have not committed. This is called miscarriage of justice.