Leviticus 5:1, 6

“When someone sins in any of these ways: If he has seen, heard, or known about something he has witnessed, and did not respond to a public call to testify, he will bear his iniquity.

He must bring his penalty for guilt  for the sin he has committed to the LORD: a female lamb or goat from the flock as a sin offering. In this way the priest will make atonement  on his behalf for his sin.