Who threw that stone? A study on DNA transfer

Area of Science:

• Forensic Science
• Trace Evidence Analysis
• DNA Profiling

Background:

• Contact DNA on stones constitutes approximately 5% of crime scene samples.
• Stone-based DNA evidence is vital in cases like burglary and property damage.
• Interpreting DNA transfer on stones presents challenges in legal proceedings.

Purpose of the Study:

• To investigate DNA transfer mechanisms onto stones.
• To differentiate between direct and indirect DNA deposition.
• To assess the reliability of touch DNA evidence from stones in legal contexts.

Main Methods:

• Experimental design involving multiple participants throwing various stones.
• Simulation of a handover scenario where one individual touched and another threw the stone.
• Analysis of DNA quantity and deposition patterns on stones.

Main Results:

• DNA transfer is primarily influenced by the individual handling the stone, not stone properties or throwing order.
• In handover scenarios, the initial toucher contributed DNA as frequently as the thrower.
• Observed DNA profiles do not definitively indicate the method of interaction with the stone.

Conclusions:

• The origin of DNA on stones cannot be solely determined from the DNA profile.
• Forensic interpretation of touch DNA on stones requires careful consideration of potential transfer pathways.
• Findings highlight the complexity of interpreting trace DNA evidence in criminal cases.