Virtue and Evil, both are like seeds. A mere single seed has the capability of turning into a giant forest if right conditions appear for it. It is similar for both virtue and evil. An extremely sacred person can give into evil if the evil has seeded deep under. Take the example of ‘Ravan’ from Hindu mythology. He was the biggest devotee of Lord Shiva but turned into a monster. Same is applicable the other way round. A devil can turn into a saint if virtue lingers deep within him.