Why is Pontius Pilate blamed for killing Jesus in the Apostles' Creed? In Apostles' Creed, the name of Pontius Pilate is forever associated with the infamy of being Jesus Christ's persecutor.


  I believe in God, the Father almighty,
  creator of heaven and earth.
  
  I believe in Jesus Christ, God’s only Son, our Lord,
  who was conceived by the Holy Spirit,
  born of the Virgin Mary,
  suffered under Pontius Pilate,
  was crucified, died, and was buried;
  he descended into hell.
  On the third day he rose again;
  he ascended into heaven,
  he is seated at the right hand of the Father,
  and he will come to judge the living and the dead.
  
  I believe in the Holy Spirit,
  the holy catholic and apostolic Church,
  the communion of saints,
  the forgiveness of sins,
  the resurrection of the body,
  and the life everlasting. Amen.


My question is, why did the authors of the Apostles' Creed include Pontius Pilate as the one who killed Jesus, and not Judas Iscariot or the Pharisees? 

From this resource I found (which I am not sure presents a convincing argument), quoting Fr. Hardon, it is because


  it has been “apostate Christians who have used the State to crucify
  the martyrs of Christianity.”
  
  Pilate symbolizes the sufferings and persecution of the Church, which
  is the Mystical Body of Christ.


That doesn't seem to explain much. Even if this explanation is true, one can still ask why did the Apostle's Creed use Pilate to symbolizes the sufferings and persecution of the Church? Why not use someone or the Roman Empire else?

So, why did the authors of the Apostle's Creed pen Pontius Pilate as the one who killed Jesus, and not Judas Iscariot or the Pharisees?
Piotr Ashwin-Siejkowski in his book, The Apostles's Creed: and its Early Christian Context, argues that Pilate was specifically mentioned primarily in order to argue for and defend the humanity and real death of Jesus.
He first emphasizes the historical importance of Pilate to Christianity:

Certainly the Scriptural detail that Jesus of Nazareth was executed under the rule of Pontius Pilate is one of the definite facts of Christianity.  His role in early Christian apologetics and also in the creeds is to bring very important historical credence.

For example, Ignatius includes Pilate's role while defending the truth of Christ's suffering:

Stop your ears, therefore, when any one speaks to you at variance with Jesus Christ, who was descended from David, and was also of Mary; who was truly born, and ate and drank. He was truly persecuted under Pontius Pilate; He was truly crucified, and [truly] died, in the sight of beings in heaven, and on earth, and under the earth. (Epistle to the Trallians, 9)

Similarly, Irenaeus mentions Pilate while defending the historicity of the crucifixion in The Demonstration of the Apostolic Preaching, 74, and Ashwin-Siejkowski summarizes Irenaeus's use of him:

In all his accounts Pontius Pilate is a recognisable evident sign of Christ's time on earth.

The wording &quot;suffered under Pontius Pilate&quot; was of significant importance to Irenaeus and others as they disputed Docetism, which held that the human form of Jesus was merely an illusion, and that he did not actually suffer.  Similarly, Justin Martyr's apologetics emphasize Pontius Pilate in order to not only prove the historicity of the crucifixion, but to demonstrate that Christ fulfilled the prophecies of Scripture (e.g., First Apology, 35).
Another early father, Tertullian, took Pilate's importance even further.  He suggests that Pilate was already secretly a Christian, and that, as the secular authority, he &quot;represents God's law and order&quot;:

To Tertullian, the emperor is the instrument of God who enforces the law as well as guaranteeing the stability of the state.  The emperor punishes crime and protects the rights of his subject. [...] Pontius Pilate was much more for Tertullian than a private person accidentally attached to the credal formula.

It's worth noting that the current wording of the Apostles' Creed developed over centuries, and that the earliest versions of it, by Irenaeus and Tertullian, mentioned Pilate. (For more on this, see Schaff, Creeds of Christendom, p53)
Summary
Ashwin-Siejkowski summarizes:

Early Christian literature [...] was very attached to, later even attracted to, the character known as Pontius Pilate.  This attachment was neither nostalgic nor marginal, as the Roman governor provided proto-orthodox Christianity with great arguments against the Docetic, then Gnostic, Jewish and pagan opponents.   Certainly Pontius Pilate in the Creeds, including the Apostles' Creed, remains as a sign of the ancient theological debate, which aimed to prove the real human nature of the Saviour, not laughing, but rather suffering Redeemer.

Compared to Judas Iscariot and the Pharisees, we can see that mentioning Pilate makes for a much stronger historical case for the crucifixion, and, at least for Tertullian, emphasizes the secular authority's role (and therefore God's role) in Christ's crucifixion.

Piotr Ashwin-Siejkowski, The Apostles's Creed: and its Early Christian Context, pages 47–55.  Italics in quotes are in the original.