Mishna, Sanhedrin 4:5 - part 1

How do they exhort witnesses testifying in capital cases? They bring them in and admonish them: Perhaps you will speak from supposition, and from hearsay, evidence from the mouth of a witness, or "We heard it from the mouth of a trustworthy person"; or, perhaps you do not know that afterwards we will test you by inquiry and examination. Know that capital cases are not as monetary suits: monetary suits - a person may give their property and effect atonement; capital cases - [the dead’s] blood and the blood of his or her offspring hang on him or her until the end of the world, for we find concerning Cain who killed his brother, it is written, "the bloods of your brother cry" (Genesis 4:10); it does not say, "your brother's blood" but "bloods" - his blood and the blood of his offspring. [Moreshet translation]