called controls, known samples, and knowns, these control samples are fully known to the forensic community with respect to composition, identification, source, and type. Examples of control samples include known combustible substances used for arson cases, known drug samples for suspected illegal drug samples, known blood types in violent crime investigations, and known DNA types for trace evidence cases.

Control samples.

Explanation:

Control samples are a kind of forensic samples which is used to confirm  analyses to obtain results which are reliable.It plays an important role in assurance procedures as well as quality control. If there is no control samples, then scientific results will produce false positives results. The results which appear true but in reality it is false. If there is no control samples then false negative results may also obtained. The results  which appear false but in reality it is true.

From a high concentration to a low concentration.