It's true that only Pilate could sentence Jesus to death but it's equally true that the Sanhedrin condemned Him to death, the latter of which holds the greater sin.
"Then Pilate said to Him, Are You not speaking to me? Do You not know that I have power to crucify You, and power to release You? Jesus answered, You could have no power at all against Me unless it had been given you from above. Therefore the one who delivered me to you has the greater sin. John 19:10-11
"Those who had arrested Jesus took him to Caiaphas the high priest, where the teachers of the law and the elders had assembled. The chief priests and the WHOLE SANHEDRIN were looking for false evidence against Jesus so that they could put him to death. (snip).... The high priest said to him, I charge you under oath by the living God: Tell us if you are the Messiah, the Son of God. You have said so, Jesus replied. But I say to all of you: From now on you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven. Then the high priest tore his clothes and said, He has spoken blasphemy! Why do WE need any more witnesses? Look, now you have heard the blasphemy. What do you think? HE IS WORTHY OF DEATH, .... - Matthew 26:59-68........"When the morning was come, ALL THE CHIEF PRIEST AND ELDERS of the people took counsel against Jesus to put him to death" - Matthew 27:1