CHICAGO (CBS) — A source close to the investigation believes a Chicago police officer who fatally shot a teenager last year will be indicted on Tuesday.

The exact nature of the charges against the officer from State’s Attorney Anita Alvarez’s office were not immediately known.

CBS 2 Chief Correspondent Jay Levine reports that Mayor Rahm Emanuel held a conference call on Monday with key civic leaders, urging calm once a video of the shooting of 17-year-old Laquan McDonald is released.

In the call, the mayor called the shooting “hideous.” The mayor said he has not viewed the video.

Emanuel told the call participants that he urged prosecutors to “make a decision so we can go as a city and begin the process of healing.”

At a news conference later on Monday, the mayor said: “You have a right to voice your opinions but do it in focused and responsible way so all voices heard.”

The timing of the dash cam video release is still not known, but a judge ordered that it be made public no later than Wednesday. Sources say the city wanted to release the video on Tuesday, but also want to wait until after an indictment is handed down.

Levine reports we may not actually see the video, which the city wanted to release tomorrow, until Wednesday, giving the state’s attorney time to act, and people time to react to the indictment before they see the video.

It was October 2014 when Officer Jason Van Dyke, who is white, shot 17-year-old Laquan McDonald 16 times on a street in the Archer Heights neighborhood. McDonald suffered 16 gunshot wounds.

Levine reports we may not actually see the video, which the city wanted to release tomorrow, until Wednesday, giving the state’s attorney time to act, and people time to react to the indictment before they see the video.

The first indication something was happening was when Alvarez missed an important campaign event Monday morning. Her nominating petitions for a re-election bid were delivered by a volunteer, instead of Alvarez herself. Unusual in that high profile politicians like Ed Burke, Dorothy Brown and Tony Preckwinkle were there, as was one of Alvarez’ challengers, Kim Foxx.

“I would imagine after 395 days and the release of the video imminent that she would be working on that case,” Foxx said.

Chicago Urban League Interim President and CEO, Shari Runner, on Monday issued a statement regarding the call for justice for Laquan McDonald:

“As we await the release of the videotape showing the killing of Laquan McDonald, the Chicago Urban League is calling for calm and mutual respect. While we understand the feelings of outrage, distrust, and fear that stem from the growing imposition of violence by police officers who are sworn to protect and serve – we are asking the community to await a thorough and transparent review of the evidence and facts to ensure justice is served. In order to honor his life, one year later, we must take meaningful action and fight for decisive change.

“The muted and too often opaque action around the killings of our youngest citizens, including Laquan McDonald, Tyshawn Lee, Rekia Boyd and hundreds of others, paints an ominous picture: In Chicago, the most segregated city in the United States, Black lives don’t seem to matter enough to police and too often to each other. Our community is in peril. What is going on in Chicago where too many unarmed Black people are subjected to disproportionate violence and killings? This is the discussion on which we need to focus.”

Chicago area pastors have said they are concerned about the video’s potentially inflammatory nature.

“Getting ahead of it, and making sure that we present to the mayor what we expect to happen, I think that’s critical if we’re going to prevent violence from happening in our neighborhoods,” said Rev. Corey Brooks, pastor of New Beginnings Church.

Brooks and other ministers and activists met with the mayor Wednesday afternoon to discuss how tamp down the potential for violence after the video is released.

“Many in our community feel betrayed, many are so very angry and protests are imminent,” said Rev. Ira Acree of Greater St. John Bible Church.

While the city originally planned to appeal the ruling to make the video public – and had argued releasing it could jeopardize an investigation of the shooting – the mayor’s office later said the city would comply with the order.

“We must try to keep this thing as calm as possible, but when the Chicago police take and slaughter a 17-year-old child, you have upset our community,” said Mark Carter, a community activist with the group ONE Chicago.

Carter said the mayor should lead an effort to make sure the officer is indicted, and should also demand the resignation of Police Supt. Garry McCarthy.

Although the mayor initially fought the effort to make the video public, he reversed course last week, and criticized the officer’s actions.

“Police officers are entrusted to uphold the law, and to provide safety to our residents. In this case, unfortunately, it appears an officer violated that trust at every level. As a result, the city’s Independent Police Review Authority promptly sent this case and the evidence to state and federal prosecutors who have been investigating it for almost a year,” he said in a prepared statement last week.

Attorneys for McDonald’s family have seen the video, and said it is shocking and disturbing, and have described the shooting as an “execution.”

“The first shot or two seem to spin him on the ground. He falls down. He’s down on the ground, and for the next 30 seconds or so, in this video, the officer just continues to shoot,” Neslund said earlier this month. “What you see are graphic puffs of smoke rising from Laquan and intermittently his body twitching, in reaction to the shots.”

The city’s police union has said McDonald was slashing tires with a 4-inch knife, and high on PCP, when he refused police orders to drop the weapon. Van Dyke has said McDonald lunged at him. His attorney, Dan Herbert has acknowledged video is graphic, but he said the officer feared for his safety, and the shooting was justified.

“He firmly believed he was in fear for his life and concerned about the life of his fellow officers,” Herbert said last week.

The city agreed to a $5 million settlement with McDonald’s family even before a lawsuit was filed. Van Dyke, a 14-year veteran, has been stripped of his police powers, pending investigations by federal and Cook County prosecutors.