Answer:
   
   Official Christian doctrine no longer holds that Jews killed Jesus,
   although it once spread that lie. Where did the notion come from? In
   the "New Testament", Jews are held in part responsible for Jesus'
   death. Some of this position comes from the fact that the disciples
   were Jewish, and it was a disciple, Judas, who betrayed him to the
   Roman authorities. Some Christian sources depict a scene in which "the
   Jews," given the choice of saving Barrabas or Jesus from crucifixion,
   chose Barrabas. However, the text doesn't tell us who :"the Jews"
   were; further, assuming this took place (which is historically
   unlikely given the Roman's behavior), they all couldn't have been
   gathered in one place. So, again, there is only indirect
   responsibility. Finally, politically, we know that some Jewish leaders
   (who were appointed by Roman Government) may have seen Jesus as a
   political threat. However, the threat was more to the Romans, and the
   Jewish leaders may have been pressured to silence him. The final
   decision lay with the Romans, who alone used crucifixion as a means of
   killing criminals and who alone had authority to impose the death
   penalty.
   
   The New Testament accounts do not agree on the story of who killed
   Jesus. The Encylopedia Judaica summarizes this as follows. In the
   first three books, the Pharisees are not mentioned in connection with
   the trial, and in John, only once (18:3). Only Mark (14:53-65;
   followed by Matt. 26:59-68) records a formal, Jewish, "night" trial
   with accusations, witnesses, and a sentence. Luke records a morning
   hearing before the Sanhedrin (Luke 22:66-71) without formal
   sentencing, and John has separate appearances before Annas (at night)
   and Caiaphas (in the morning) who conducts an interrogation (18:12-
   24). In the entire book of Luke (not just in his description of the
   Passion) there is no mention of the Sanhedrin's verdict against Jesus,
   and John records nothing about an assembly of the Sanhedrin before
   which Jesus appeared. Hence, it seems very probable that no session of
   the Sanhedrin took place in the house of the high priest where Jesus
   was in custody, and that the "chief priests and elders and scribes"
   who assembled there were members of the Temple committee (see also
   Luke 20:1): the elders were apparently the elders of the Temple and
   the scribes were the Temple secretaries. The deliverance of Jesus into
   the hands of the Romans was, it seems, the work of the Sadducean "high
   priests," who are often mentioned alone in the story. A man suspected
   of being a messianic pretender could be delivered to the Romans
   without a verdict of the Jewish high court. In addition, the high
   priests were interested in getting rid of Jesus, who had spoken
   against them and had predicted the destruction of the Temple. Mark
   offers some clues to the historical situation. The public reason given
   in the placard on the cross (Mark 15:26), recorded in all four
   Gospels, was that Jesus claimed to be a king, which for the Romans was
   tantamount to sedition. Those crucified with Jesus are called
   "revolutionary bandits". Jesus teaching on the kingdom, his
   association with marginal groups in his society, and his attacks on
   abuses associated with the Temple made him suspect to both Romans and
   the Jerusalem aristocracy. Though some interrogation may have taken
   place before Jewish authorities, the Romans bear the responsibility
   for any formal trial. All the texts agree that the Roman prefect,
   Pontius Pilate (a.d. 26- 36), ordered the execution (also attested by
   the Roman historian Tacitus, Annals 15.44). The execution was in the
   Roman way, by crucifixion. All the books indicate that on the third
   day after the crucifixion Jesus' tomb was found empty. According to
   Mark an angel announced that Jesus had risen, and the other books
   state that Jesus appeared before his believers after his death.
   
   Jewish laws on capital trials are found in texts almost two centuries
   after the death of Jesus (M. Sanh. 4-11), so it is not known whether
   they reflect first-century practice. By these norms the trial in Mark
   is not legal, since according to the Mishnah capital trials could not
   be held at night or on the eve of a Sabbath or feast day (M. Sanh.
   4:1). The sentence of death could not be pronounced on the same day as
   the trial (M. Sanh. 4:1); prior examination of witnesses, as well as
   independent agreement of their testimony, was required (M. Sanh. 4:5;
   cf. Deut. 19:15-18); the charge of blasphemy required the explicit
   pronouncing of the divine name (M. Sanh. 7:5); and trials were to be
   held in the official chamber, not in the house of the high priest (M.
   Sanh. 11:2; cf. Mark 14:54). Also uncertain is whether the Sanhedrin
   had the power to execute for capital offenses during Roman occupation
   (see John 18:31). If so, Jesus should have been stoned, which was the
   Jewish penalty for blasphemy.
   
   We also know that the early Christians who wrote the story wanted to
   make the Romans appear less guilty.
   
   Another factor to consider: It was Jesus' resurrection that began
   Christianity. If the Roman's hadn't killed Christ, he wouldn't have
   had the opportunity to rise (if you hold with the resurrection). In
   fact, in the texts, Jesus claims all responsibility, and is explicitly
   the "willing Suffering Servant" Christian theology is that Jesus'
   entire purpose was to come to die.