The Father is at the investigative judgment. But the Father has chosen Christ to serve as judge. The Father leaves all judgment of sin to his son. Many people do not feel comfortable when the judgment is discussed. He will prove to the people of the world that they are wrong about sin.
All men realize they are responsible for their actions.
The work of the Holy Spirit is to teach men that they are doing wrong. Man was created to live in harmony with God's way of life. When man does not follow God's plan, his conscience bothers him. People who refuse to listen to their conscience and the Holy Spirit know they are wrong. So these people spend their lives running from their conscience.