Deuteronomy 21:23 "His body shall not remain all night upon the tree"

Man was created in the image of HaShem and we must respect the body of a human being, even if he is no longer alive.

At times, a Beit Din may order the execution of a criminal and, after his execution, have the corpse hung as an example to the people. (See Positive Mitzvah 230). The corpse may not be left hanging overnight. Rather we must take the body down before sunset and bury it on the same day.

This law also applies to anyone that passes away.

We are forbidden to delay the burial to the next day, except in cases where it is required for respect and honor of the dead person. In a case where arrangements for the funeral have to be made, or relatives and friends need time to get to the funeral, such a delay is permissible.