Leviticus 4:15

(15) And the elders of the congregation shall lay their hands.—As the whole congregation could not lay their hands on the victim, their representatives had to perform this act. (See Leviticus 4:4.) But as the elders also were far too many to do it, since they were seventy in number, it was ordained during the second Temple that three of their members should lay their hands upon the sacrifice. Besides this sin offering there was only one other congregational offering upon which there was this laying of hands: i.e., the scape-goat (Leviticus 16:21).