It was the Romans that crucified him. However, the Sanhedrin (Jewish Coucil) wanted him killed at the time due to crimes of Blasphemy which under Jewish law was deemed to be punishable by death (The Irony is, that he was God, supposedly anyway). Under Roman occupation they didn't have the authority to commit such an act though. So instead the Jewish leaders presented him to the Romans as someone who was likely to cause Jewish rioting. They managed to persuade Pontius Pilate (Roman Leader) to make the decision to have him executed as he was a threat to the Roman state.