It has long been an interpretation by some within the Church, as well as in other Christian denominations, of Mathew 27:25 “His blood be on us and on our children” that the Jews are collectively responsible for the death of Christ. This stems from a too-literal reading of that Gospel account, and an ignorance of Church teaching.
That his death was the responsibility of all humanity, including Christians, was emphasized at the Council of Trent, and again at Vatican II.
John Paul II deserves credit not for changing the Church’s position on this, which he did not, but for being more proactive in reaching out to Jews, and apologizing for past sins of the Church in its treatment of Jews.