REID: For three straight days people have taken to the streets of East Pittsburgh to protest the fatal shooting of 17-year-old Antwon Rose by police. Rose was shot Tuesday while attempting to go flee a car that had been stopped by police because it matched the description of a vehicle involved in a nearby shooting. Rose was unarmed, though police say they found an empty clip in his pocket and two guns in the vehicle. The video of him getting shot as he ran away has sparked outrage, and we want to warn you, you will find it disturbing. (shows video) The officer who shot Rose had been sworn onto the East Pittsburgh police force for just hours - HOURS - before the shooting. He's now on administrative leave. Back with me to discuss, Lawrence O'Donnell, host of MSNBC's "The Last Word, and the author of "Deadly Force, A Police Shooting and My Family's Search for the Truth." It was recently republished in paperback with a new preface. Congratulations. I was bragging I have an old school version of the book.

O'DONNELL: It's actually, the original is over 30 years old. One of the sad things to report is I've been on this subject for 35 years. And the only thing that has changed is that we now have video like that. That video didn't exist for 35 years.

REID: Why doesn't that video change the outcome in these cases?

O"DONNELL: It's going to have a very powerful effect on the outcome for a bunch of reasons. That's going to be the crucial piece of evidence for the District Attorney studying this already. After -- this book first came out in 1983. The next year, the year after this book came out, the Supreme Court ruled it unconstitutional to make it legal to shoot fleeing felony suspects, because a bunch of states at that time, not all of them, but a bunch of states had laws that specifically state that it's legal to shoot a fleeing felony suspect. All they have to do is flee.

REID: Yeah.

O'DONNELL: The Supreme Court said, "No, that's an unconstitutional law, you can't do that." So, now, the justification for shooting has to be some threat to someone and by definition, unarmed fleeing suspects are not a threat to anyone.

REID: Yeah.

O'DONNELL: The police officers' stories, always in these cases, almost always would carry this phrase: "He turned in a threatening manner as if to shoot." I have seen that phrase word for word in countless police reports over decades and without that video, "He turned in a threatening manner as if to shoot" would work as a complete defense and it doesn't matter after the fact if it turns out he didn't have anything this his hand or he had a phone in his hand or had a toy in his hand, but that video shows someone running away, being shot at while running away. The autopsy is going to come out. The autopsy very likely is going to show entrance wounds in the back and the story in my book, the entrance wounds when the autopsy comes out are in the back and the back of the head and the back of the neck, and that kind of information is going to determine where this case goes. It's a very, very -- I don't -- it's not clear to me at this stage what the defense would be here. Police officer has been suspended, which is the correct decision. If you had to bet in this case, I would bet it is going to go against the police.