On the historical reliability of Mark 6:27

I also first published this question in BHSE, but it’s relevant to historical investigations into Christianity, can anyone help me to understand this below? Mark’s Gospel is often considered the earliest gospel written by scholars. We read: > “Immediately the king[*Herod*] sent a soldier of the guard with orders > to bring John's head. He went and beheaded him in the prison,” ‭‭Mark‬ > ‭6‬:‭27‬ ‭NRSV‬‬ But British scholar F.F. Bruce records this information: (A Baraitha from the period of 70A.D.-200A.D. named "TJ Sanhedrin 1.1" says:) > "forty years before the destruction of the temple the right to inflict > the death penalty was taken away from Israel." > -Source: "Jesus and Christian Origins Outside the New Testament" by F.F. Bruce (page 56, footnote 5). **Question:** How is Mark 6:27 historically reliable given that Herod killed John the Baptist in Prison but likely didn’t have authority to execute capital punishment given the information in the Baraitha?