Evidence that can be described as ˮscientific evidence” is of increasing importance in criminal trials due to the dynamic development of forensics. These evidences can be highly damaging circumstantial evidence and prejudge the outcome of the trial. The article highlights the importance of ˮscientific evidence” for the defendant’s situation and indicates the premises of an effective defense tactics in trials where such evidence may be of key importance. The publication uses own research carried out in order to write a doctoral dissertation on defense tactics. The article points out that an incorrect interpretation of the meaning of the results of identification tests or a wrong conclusion of the identification opinion may constitute a real danger for the accused, i.e. lead to the conviction of an innocent person.