Experimental evaluation of the impact of reduced anticontamination measures on the integrity of items sampled within mock crime scenes

• DNA testing of CSI equipment brings no value to reduce contamination of evidence. • CSI professional judgement is most critical to reduce the risk of contamination. • Mitigations to reduce DNA contamination should be proportionate to the risk. • DNA transfer from an item of CSI equipment to crime scene evidence is low. Crime Scene Investigators (CSIs) in the UK conduct extensive anticontamination measures to mitigate the risk of introducing extraneous DNA into forensic evidence. This study empirically evaluated the effectiveness and proportionality of such measures, focusing on equipment cleaning and glove-changing practices during evidence recovery in mock crime scenes. The experimental design deliberately introduced contamination risks, such as the use of contaminated equipment, transport containers, and gloves and included both standard and streamlined (reduced glove changes/cleaning) procedures. Six CSIs from two police forces recovered 24 biological samples (semen, blood, saliva, and touch DNA) from two mock scenes. Critically, no extraneous DNA profiles were detected in any evidential samples, even under deliberately compromised conditions or when streamlined practices halved the time required for recovery. These findings indicate that many current anticontamination measures exceed what is necessary to protect evidential integrity. The results support a more proportionate, risk-based approach, suggesting that UK police forces could safely reduce certain anticontamination practices without compromising the quality of forensic evidence. Further research in real-world settings is recommended to confirm these conclusions and guide policy.