Determination of semen stain age on different fabric types by FT-IR spectroscopy

Body fluids such as blood, semen, vaginal secretions, and saliva are frequently encountered at the crime scene. In sexual assault crimes, one of the most reliable biological evidence is semen stain. Age determination of the semen stain plays an important role in both confirming sexual assault, identifying suspects, and estimating the time frame in which the crime occurred. It is aimed to develop a method to determine the time of formation by using Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy for up to 8 weeks in semen stains dripped on five different fabric types. High R2 values and low root-mean-square error (RMSE) were obtained in models constructed using Principal Component Analysis (PCA) and Partial Least-Squares Regression (PLSR). Although it varies according to fabric types in modeling, it has been observed that age estimation can be made with an interval between 0.18-0.32 days in the range of 0-3 days, between 0.56-1 days in the range of 3-7 days, between 2.66-3.96 days in the range of 1-4 weeks, 4.74-6.56 days in the range of 4-8 weeks. In this thesis, it has been shown that ATR-FTIR spectroscopy combined with chemometrics can be an effective method for estimating the age of human semen stains on different fabric types based on time-dependent changes in the spectrum.