What does Acts 4:6 mean?
Acts 4:5 says the group includes rulers, elders, and scribes. It doesn't mention the priests, which make up a significant portion of the Sanhedrin. It was Annas and Caiaphas who led the Jewish trials of Jesus (John 18:12–13, 28). It's possible the priests are the driving force behind persecuting Peter and John now.Annas had been high priest from AD 6–15, but he held great power for a long time after. Five of his sons went on to be high priest and Caiaphas is his son-in-law. Even when Annas was not high priest, he assumed privileges, like being the first to question Jesus after His arrest (John 18:12–13). Here, he seems to be the leader of the influential priests, including Caiaphas who is still the ruling high priest. Annas seems to have been very much involved in Caiaphas' duties. Luke says that John baptized Jesus "during the high priesthood of Annas and Caiaphas" (Luke 3:2). But it was Caiaphas who told the Sanhedrin to arrest Jesus after He raised Lazarus from the dead (John 11:49–50).
When Peter boldly claims his audience crucified Jesus, he doesn't mean it in a vague, corporate way as he did when speaking to the crowds in Acts 2 and 3. He explicitly means Annas, Caiaphas, and the other Sanhedrin members who personally orchestrated the murder of their own Messiah.
We don't know who Alexander and John are. Presumably Alexander is not the same man mentioned in Mark 15:21, Acts 19:33, or 2 Timothy 4:14. John may be Annas's son Jonathan who goes on to be high priest, but we don't know.