AIMS: The present study investigates the efficiency of biological samples taken from the crime scene on crime detection.

METHODS. This study is a descriptive, documentary and applied. The statistical population of this research includes 60 employees of Zanjan State Criminal Police, including crime scene investigators, lab experts of forensic chemistry and biology, forensic detectives, medical examiners and examining magistrates and prosecuting attorneys of Zanjan province’s Judicature with at least 5 years of executive experience in crime scene investigation. The questionnaire is used as a tool in this study. The validity of the questionnaire was confirmed by the experts and the reliability of the questionnaire, calculated by the Cronbach's alpha coefficient, was 0.939. For analyzing, descriptive and inferential statistics Kolmogorov-Smirnov, Friedman and one sample t-tests were used. The Kolmogorov-Smirnov test showed normal distribution of the data; so the parametric tests were used to examine the variables.

FINDINGS. The results of one sample t-test showed that biological samples of blood, saliva, semen, and hair strand make a significant contribution to the scientific detection of crime. Friedman test for ranking the importance of various factors related to different samples on crime detection rate from the view of the respondents, showed that using modern equipments and technologies, sample quality and officer scientific and technical knowledge have the most priorities.

CONCLUSION. According to the results the best biologic test, from the view of the respondents, in crime detection is DNA typing.