A graphic video released this week showing a white police officer fatally shooting a black teen in Chicago 13 months ago has raised questions about how this case has been investigated and prompted pleas for protesters to show restraint.

So far, the streets of Chicago have not seen the kind of violence that followed the deaths of other black teens at the hands of white police officers elsewhere  in the U.S.

Still, there are many outstanding questions regarding the case of Laquan McDonald, whose death has now led to a first-degree murder charge against Chicago police officer Jason Van Dyke.

1. Why did it take so long for the video to be made public?

McDonald was shot on Oct. 20, 2014. A judge last week ordered that the dash-cam video be released, and it was made public on Tuesday.

"To me, the first question is why it was kept from the public for so long," says Craig Futterman, a professor at the University of Chicago Law School.

Futterman, one of the lawyers who brought the Freedom of Information Act case to seek the video's release, questioned the elapsed time particularly because there has been an ongoing conversation throughout the U.S. on race and policing. 

Chicago protests after Laquan McDonald's death

A woman greets protesters out of a car window during a protest after the release of a video showing the shooting of Laquan McDonald in Chicago. (Andrew Nells/REUTERS)

"There's no way you earn any trust without honesty," he said, noting the "best practice" is releasing videos like the one in this case within 24 to 48 hours.

"There was absolutely no reason not to here."

The Chicago Police Department said the city wouldn't release the video because "we did not want to do anything that might interfere with the ongoing investigation."

Philip Stinson, a criminologist at Bowling Green State University in Ohio, says there are situations where it would be ethically inappropriate for a prosecutor to release inflammatory evidence before a trial.

"You could have a situation where a defence attorney later says, 'Well, the jury pool has been tainted by the video. You shouldn't have released the video.' You run into all these types of problems, so it doesn't surprise me at all that the video wasn't released for a long time."

In other instances, however, videos — ones that might shock the public conscience or be inflammatory — have been released.

That can happen, Stinson says, "in an effort to be transparent and to let the community understand that they are taking these matters seriously so as to keep situations and social justice activists and people in the community from rioting.

"But that could come back to haunt the prosecutors later on if it impacts on the defendant's ability to get a fair trial. So it's a complicated issue, and we can all speculate as to what the intent was."

2. What about the Burger King video?

A Burger King near where McDonald was shot had a security camera trained on the area where the incident occurred.

But some video from the night in question is missing, with NBC News in Chicago reporting that earlier this year, a district manager for the food chain said police officers deleted footage from the camera.

Eighty-six minutes of footage is missing, covering the time McDonald was shot, NBC reported, citing lawyers from McDonald's family.

Futterman says seven video files showing seven different angles of the scene were deleted by an officer. Burger King's "surveillance tape was actually running while he erased the files, so while the videos of what happened before [the shooting] are gone and erased, there is a video of the officer erasing the videos."

Cook County state's attorney Anita Alvarez said forensic testing was done on the surveillance footage from the restaurant and no evidence of tampering was revealed, NBC also reported.

3. What about the first police reports of the shooting?

In initial reports of the incident, police said McDonald refused orders to drop a knife and walked away from them. The police union has also said the teen lunged at officers with the knife.

Killings by Police Chicago

Chicago police Officer Jason Van Dyke was charged Tuesday with first-degree murder in the slaying of 17-year-old Laquan McDonald. (Associated Press)

The video released Tuesday [WARNING: GRAPHIC CONTENT] shows McDonald jogging down an empty lane on a four-lane street and veering away from Van Dyke and another officer who emerge from a police SUV drawing their guns.

Within seconds, Van Dyke begins firing. McDonald spins around and falls to the pavement as Van Dyke keeps shooting.

"This case shows more than anything else the power and reality of the police code of silence in Chicago," says Futterman, adding that "immediately after the killing, more police arrive on the scene in response to this shooting and immediately the code of silence goes into effect [and] a false narrative is shared with the media by representatives of the Chicago police."

4. Can a first-degree murder charge stand up in this case?

Futterman says the laying of the first-degree murder charge against Van Dyke is "historic" for the city, which sees about 50 shootings by police a year.

"There hasn't been a single instance since 1968, so nearly 50 years ago, when a Chicago officer was criminally prosecuted for shooting any man, woman or child while on duty."

And it doesn't happen that often elsewhere in the U.S. either.

Stinson, whose research has delved into police crime and integrity, says the "best estimate we have" is that about 1,000 times a year, an on-duty police officer shoots and kills a person somewhere in the U.S.

He says his research also shows that from 2005 until the end of 2014, 47 non-federal, sworn law enforcement officers — police officers, deputy sheriffs and state troopers — were charged with murder or manslaughter resulting from a fatal on-duty shooting.

Of those 47 cases, about 23 per cent resulted in a conviction of some kind, says Stinson.

"It seems to be that juries are very reluctant to second-guess the split-second, life-or-death decisions that a police officer makes in a violent street encounter."

So far this year, 15 officers have been charged in the U.S., with video playing a key role in nine of those cases, he says.

Killings By Police Chicago

Chicago Mayor Rahm Emanuel, left, and Police Superintendent Garry McCarthy appealed for calm following the release of a video that shows a police officer fatally shooting 17-year-old Laquan McDonald. (Charles Rex Arbogast/Associated Press)

"What we're seeing in the last year or two is that in some of these cases there's video evidence that directly contradicts initial statements made by officers on the scene, and directly contradicts written reports and written statements," he says.

"If it weren't for those videos, I just do not think the officers would have been charged with murder or manslaughter."

5 .What about the reporter who pushed hard for the dash-cam video's release?

When the dash-cam video went public earlier this week, the journalist whose lawsuit led to its court-ordered release didn't have a chance to attend the news conference and ask any questions.

The New York Times reported Wednesday that freelance reporter Brandon Smith said he was barred from attending the session with Mayor Rahm Emanuel and Police Superintendent Garry F. McCarthy.

"To be left out feels punitive and disrespectful," says Futterman, who represents Smith.

The Times reported that police officials did not answer email and phone requests for comment on the issue.

With files from The Associated Press