Other mistake: The crow leads Eric along a rooftop at the start in the pouring rain and down into a building. However, as Eric is walking into the building there are no wet marks from his soaking wet boots. (00:10:00)
Other mistake: When the girl is kidnapped and Eric goes to save her, he enters a big door of that Gothic cathedral (as depicted on the movie cover). At that moment, the wind blows. But for the scene to make any sense, the wind should blow from the outside in, not from the inside of the church out, but the motion of Eric's hair shows the wind blowing the wrong way. (01:05:55)
Answer: There is no explaination given in the films, they are just brought back when the crow feels it is the right time to avenge their murder.