In his most thorough admission of the church's guilt in the clerical sex abuse scandal, Pope Benedict XVI said Tuesday the greatest persecution of the institution "is born from the sins within the church," and not from a campaign by outsiders. The pontiff said the Catholic church has always been tormented by problems of its own making — a tendency that is being witnessed today "in a truly terrifying way." "The church needs to profoundly relearn penitence, accept purification, learn forgiveness but also justice," he said. "Forgiveness cannot substitute justice," he said. Benedict was responding to journalists' questions, submitted in advance, aboard the papal plane as he flew to Portugal for a four-day visit.