CNN guest schools ex-cop over Laquan McDonald shooting video: Your claims violate the laws of physics!
Marc Lamont Hill and harry Houck (CNN)

Chicago is bracing for the release of video showing the police killing of 17-year-old Laquan McDonald -- which some observers fear could tear the city apart.

A judge set a Wednesday deadline for city officials to release the video -- which has been described as depicting an execution -- but CNN's police expert has already made up his mind without seeing the video himself that Officer Jason Van Dyke was justified in shooting the fleeing teenager multiple times in the back.

"The fact is, this gentleman did have a knife in his hand," said Harry Houck, a CNN contributor and former New York City police detective. "This could come down to experience, I don't know. The fact is that apparently they followed this man for almost half a mile with a knife."

"New Day" host Michaela Pereira reminded the contributor that McDonald was a teenager, not an adult.

"A teenager would kill me just as dead as a 30-year-old," Houck said. "He had a knife in his hand and he was under the influence of PCP, which is a psychotic drug that makes you go crazy."

He said officers should have feared that McDonald might encounter and then violently attack a random civilian, and Houck disagreed that police could have set up a perimeter around the teen and then arrest him.

"You can't shoot somebody for a hypothetical citizen who never entered the fray," said Marc Lamont Hill, a CNN political contributor. "The other five officers were there, and they didn't perceive a threat."

Hill said Van Dyke inaccurately claimed after the shooting that McDonald was approaching him with a knife, although those who have seen the dashboard camera video say it shows the officer repeatedly shoot the teen as he lay face-down on the ground.

"That raises serious questions about the veracity of his claims," Hill said.

Houck said officers must act quickly to eliminate potential threats.

"I don't know if, all of a sudden, I'm sitting there playing stupid, silly games, this guy comes this way here, and he kills an officer -- when I could have shot him five minutes ago," Houck said.

Houck said the officers were trying to contain McDonald when one of them opened fire, but he said Van Dyke was likely justified because the teen could have cut them with the four-inch knife he was carrying -- even from 10 to 15 feet away.

"Ten to 15 feet -- wow," Hill said.

"I'm not exactly sure of Harry's sense of physics here and distance, but a four-inch knife 15 feet away -- I'm not sure how you can cut someone, particularly if you're running away from them, just based on the laws of physics," Hill continued. "Harry, I don't need to be an expert to know that a knife this long can't cut somebody from 15 feet away unless it's a super knife or you throw it."

Houck argued that McDonald could have run at officers and stabbed them.

"But my point is, Harry -- he was running the other way," Hill said.

Houck said he needed to see the video before determining what the threat the teenager actually posed.

"That's my point," Hill said. "You have an extraordinary amount of insight into what the police officer was thinking, that the police officer didn't break any rules, even though you haven't seen the video. My claim isn't on what's on the video -- my claim is that if an officer says one thing and then later on a video shows the guy was running the other way, that calls into question the claims that he made."

Watch the entire segment posted online by CNN: