Final answer:
Witnesses are the main source of information for relays, providing crucial testimonies and observations in legal proceedings.
Step-by-step explanation:
The main source of information for relays in the context of your question would be witnesses. Witnesses play a crucial role in providing testimonies and sharing their observations regarding a crime or incident. Their memory and account of the details can be important in identifying suspects and prosecuting criminals. However, it's important to acknowledge that eyewitness testimony can sometimes be flawed or influenced by external factors, which is why the reliability of such testimony is a subject of debate in legal proceedings.