If the Sanhedrin didn’t dare kill Jesus and took him to Pilate to honor Roman authority in capital cases, why did they dare kill Stephen (Acts 7)?
Judea was under Roman law, and the Sanhedrin didn’t have the right to inflict the death penalty (John 18:31). Multitudes clearly viewed Jesus as a great prophet and possible Messiah. (Mark 11:1-11 and Luke 19:28-40 describe how the people welcomed Him into Jerusalem.) Furthermore, Jesus’ friends were not limited to the poor (Matthew 9:18; John 3:1-2; John 12:42; John 19:38-39).
A mob might have been able to kill Jesus spontaneously without serious political consequences. (Luke 4:16-30 describes such action by a mob.) But because of Jesus’ notoriety and popularity, the Jewish religious and political leaders couldn’t arrest and execute Him—or even have Him assassinated—without potentially serious repercussions.
So the reason the Jewish leaders used Pilate to carry out Jesus’ death was probably not because they feared and respected Roman law, but because they feared the people (Mark 12:12; Luke 22:2).
Once Jesus was dead, however, the Sanhedrin could assume there would be little likelihood of a popular uprising against them. Although Stephen was a beloved figure in the church, he didn’t have Jesus’ fame and popularity with the masses. The Romans were unlikely to pursue any political action against the Sanhedrin because of the murder of one Hellenistic Jew by a religious mob.