Yevamot, Chapter Sixteen, Mishnah Three
This mishnah provides rules of what a witness needs to see in order to testify that someone is dead.
1) They are allowed to testify only about the face with the nose, even though there were also marks on the mans body or clothing.
2) They are allowed to testify only when his soul has departed, even though they have seen him cut up or crucified or being devoured by a wild beast.
3) They are allowed to testify only [if they saw the body] within three days [of death].
4) Rabbi Judah ben Baba says: not all men, all places, or all times are alike.
Section one: A person is identifiable only through his face and his nose. Therefore, if someone sees other parts of his body or face, but not his face and nose, he cannot testify that the person is dead.
Section two: The person must already be dead in order to establish testimony of his death. It is not sufficient to see him being cut up, crucified or devoured by a wild beast. Even though his imminent death in these situations is nearly certain, this is not sufficient.
Section three: The witness must testify within three days of the death. Otherwise the body may begin to decompose and identity cannot be provided with certainty.
Section four: According to Rabbi Judah ben Baba it is impossible to set uniform rules for identifying bodies. Some mens faces will change quicker than others at death, in some places decomposition will take place quicker, and much depends on the time of year as well (rain or sun). Therefore each situation must be ruled upon based on the circumstances of that situation.