Note 4 at Jn. 18:31:The Jews had tried to put Jesus to death many times before (see ref. j at this verse) as well as other people (Jn. 18:3-7). They succeeded in stoning Stephen to death (Acts 7:59), which was the method of execution prescribed by Moses in the Old Testament (Jn. 8:5) and apparently allowed by the Romans. However, here they say that it was unlawful for them to put any man to death. This was just not the truth.

Since Jesus had overcome every attempt of the Jews to kill Him and since His popularity had grown to the point that one of these Jews had said, "the world is gone after him" (Jn. 12:19), it is probable that these Jews were just seeking the superior power of the Roman army to do what they couldn't do.

However, without them knowing it, they were helping to fulfill the prophecy of Jesus where He specified the type of death that He would die (see note 10 at Jn. 12:32, p. 358). Jesus had to be crucified to redeem us from the curse of the law (Gal. 3:13).