Aaron did not act according to the ordinary Law Leviticus 4:5-7, Leviticus 4:16-18, but as Moses had done in the sin-offering of the consecration ceremony (Leviticus 8:15; compare also Leviticus 4:25, Leviticus 4:30, Leviticus 4:34). The probable reason of this was that he had not yet been formally introduced as the high priest into the holy place of the tabernacle.
Brought the blood - They most likely held the basons in which the blood was received as it ran from the victim, and then handed them to their father. See Leviticus 1:5.