Eric Draven: It can't rain all the time.
Sarah: People once believed that when someone dies, a crow carries their soul to the Land of the Dead. But sometimes, something so bad happens that a terrible sadness is carried with it and the soul can not rest. Then sometimes, just sometimes, the crow can bring that soul back to put the wrong things right.
Albrecht: Police! Don't move! I said, don't move!
Eric Draven: I thought the police always said freeze.
Albrecht: Well, I am the police, and I say, "Don't move" Snow White. You move, you're dead.
Eric Draven: And I say I'm dead and I move.
Top Dollar: Caw, caw! Bang! Fuck, I'm dead!
Albrecht: Say? Are you some kind of...of ghost?
Eric Draven: Boo.
Eric Draven: Mother is the name for God on the lips and hearts of all children.
Sarah: If the people we love are stolen from us, the way to have them live on is to never stop loving them. Buildings burn, people die, but real love is forever.
Funboy: Jesus Christ!
Eric Draven: Jesus Christ? Stop me if you heard this one. Jesus Christ walks into a hotel. [Fun Boy shoots him.] He hands the innkeeper three nails, and he asks... [Fun Boy shoots him again.]
Funboy: Don't you ever fucking die?
Eric Draven: Can you put me up for the night?
Eric Draven: Suddenly, I heard a tapping. As if someone gently rapping. Rapping at my chamber door.
Gideon: What are you talking about?
Eric Draven: You heard me rapping, right?
Albrecht: At least he didn't do that walk against the wind shit, I hate that.
Albrecht: You the one who killed Tin-Tin?
Eric Draven: He was already dead. He died one year ago, the moment he touched her. They're all dead. They just don't know it yet.
Eric Draven: It's not a good day to be a bad guy, huh, Skank?
Skank: I ain't Skank. That's Skank over there! Skank's DEAD!
Eric Draven: That's right. [Throws Skank out of the window.].
T-bird: One of my crew got himself perished.
Top Dollar: Which one?
T-bird: Tin Tin. Someone stuck all his knives in his internal organs in alphabetical order.
Eric Draven: Is that gasoline I smell?
Tin Tin: What the fuck you all painted up for, crackhead, huh? Halloween ain't till manyana.
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.