Their blood shall be upon them— Compare Deuteronomy 19:10. The plain meaning of the phrase is, their blood shall be chargeable upon themselves: the punishment of them shall acquit the land from guilt; see Matthew 27:25.
Related Commentaries of Leviticus 20:11
Leviticus 20:11
11 And the man that lieth with his father's wife hath uncovered his father's nakedness: both of them shall surely be put to death; their blood shall be upon them.