He traded bullets for petals. Someone laying flowers on Pope John Paul II’s tomb isn’t unusual. But when it’s the former Turkish nationalist who shot the pontiff in 1981, it’s remarkable. Mehmet Ali Ağca opened fire on the pope’s car, leaving John Paul II in critical condition and giving rise to the bulletproof “Popemobile.” After three decades in prison — where the pope visited and forgave him — Ağca was released in 2010. His gesture echoes loudly against the backdrop of a changing Catholic Church.