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)
Audio problem: There is a scene where Eric is following the crow through a dark room. The camera trails off to show the crow's shadow and there is a sound as of wings fluttering yet the shadow is perfectly still. (00:10:10)
Continuity mistake: Top Dollar shows a snow globe to a female companion near the start. Her grip on the snow globe changes instantly. In some shots she has her fingers on the glass and not in others. (00:23:35)
Continuity mistake: When Sarah is skateboarding, and the guy in the car yells at her to get out of the road, she pushes with her right foot and has her left foot in front (a "Regular" stance), but in the next shot she is riding "goofy" stance (right foot front), with no time to change stances. (00:24:25)
Continuity mistake: Eric smashes the door to Gideon's Pawn Shop and stays outside. The shot shows Gideon on the floor then Eric about 6 foot inside the door. Not enough time has passed for him to get that far. (00:26:00)
Continuity mistake: When Eric is about to leave Gideon, he points the shotgun at him, then holds it vertically. Just after he says "your job is to tell the rest of them..." we see a shot of Gideon, and the barrel of the shotgun is visible in the top left corner, pointing at him again. Back to Eric, and the shotgun's still vertical. (00:30:00)
Continuity mistake: Officer Albrecht gets out his car and takes aim at Eric from behind the car door. The camera changes and Albrecht is walking forward without closing the car door or going round it. (00:30:50)
Continuity mistake: After Eric spreads petrol (or something ignitable), he leaves Gideon's Pawn Shop with the shotgun full of rings. When standing outside, he shoots the shotgun into the building. First of all, I doubt that even petrol could make such a big explosion. Secondly, if you watch closely, the top of the building seems to blow up before the bottom. (00:31:05)
Visible crew/equipment: When Eric disappears for the first time the camera spins around on Albrecht. In this shot, the shadow of the camera can be seen at his feet. (00:31:50)
Continuity mistake: When Funboy gets shot in the leg it hits his right, he is then shown clutching his bloody left leg and then his right when he is dragged into the bathroom. It goes back and forth like this. (00:38:20)
Visible crew/equipment: When Lee shoots Fun Boy, Fun Boy falls backwards on to the bed. His leg flies up, and you can clearly see the cord coming from his pants that is attached to the fake blood bag. (00:39:05)
Continuity mistake: When Eric puts Fun Boy in the tub and runs the water on him the shower head changes position between shots. (00:40:25)
Continuity mistake: When Gideon is in the bar, he takes the top off the bottle just as the other bloke grabs it. The second bloke then proceeds to take the top off the bottle again. (00:41:35)
Continuity mistake: The can Albrecht drops on the floor when Eric visits moves places without anyone touching it. When Eric says about the hat still being on it's on the wooden flooring. When he walks past to read the file a few minutes later the can is on the carpet. (00:43:25)
Continuity mistake: When officer Albrecht shows the Shelly Webster file to Eric before the "nothing is trivial" conversation, the police hat changes position over the table in every shot. (00:44:30)
Audio problem: When Albrecht asks to Eric if he is going to vanish into thin air again, the shot changes and Albrecht still is moving his mouth but now he is voiceless. (00:46:30)
Revealing mistake: When Draven sends T-bird to his death in his car, the real Ford Thunderbird is replaced by a fake mockup using a flimsy one-piece fiberglass body mounted on a pair of straight axles. When it explodes, the body lifts off in one piece, warping wildly while the front axle simply falls away. No proper car components like engine, transmission, suspension and so on, are seen anywhere, though they should be. (00:57:05)
Continuity mistake: When Darla prepares breakfast for Sarah, the bottle of juice on the table changes positions between the shots. (00:58:50)
Continuity mistake: When Sara is going to the abandoned building and takes off some wood pieces, the gap between the pieces increases between shots. (01:01:00)
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.