The trial of three Chicago Police officers accused of falsifying reports to shield fellow officer Jason Van Dyke from punishment for the 2014 shooting of Laquan McDonald began Tuesday at the Leighton Criminal Court Building. Here are some basics before opening statements begin.

What is this case about?

Jason Van Dyke shot 17-year-old Laquan McDonald 16 times the night of Oct. 20, 2015. In October, Van Dyke was convicted of second-degree murder and 16 counts of aggravated battery for the shooting, and this trial will cover what happened afterward as the Chicago Police Department investigated the slaying. The murder charge against Van Dyke came more than a year after the shooting, announced on the same day that video of McDonald being shot was released to the public. But by then, Van Dyke had already been cleared of wrongdoing by the police department — despite the fact that it appeared federal investigators were probing the shooting soon after it happened.

Related: A complete guide to the Jason Van Dyke trial and conviction in the murder of Laquan McDonald

Former judge and federal prosecutor Patricia Brown Holmes was appointed to probe the shooting, after activists lobbied to have a special prosecutor lead an inquiry of how the police and the State’s Attorney’s Office handled the McDonald investigation. After an 11-month investigation, Holmes announced charges against three other officers in an alleged cover-up. The trial itself may delve into suspect behavior by numerous additional officers who were not charged but who were at the scene or involved in the investigation that followed.

Who is on trial?

Two officers who were at the scene and the detective who led the Chicago Police investigation of the shooting.

Thomas Gaffney and his partner were the first officers to encounter McDonald the night of Oct. 20, 2014 after a caller to 911 reported the 17-year-old was breaking into trucks on a Southwest Side lot. His partner, Joseph McElligott, who was not charged in the case, followed McDonald on foot, and Gaffney tailed McDonald in his police SUV, which McDonald stabbed in the tire and windshield after Gaffney tried to cut him off. McElligott is expected to testify for the prosecution.

Joseph Walsh was Van Dyke’s partner the night of the shooting, though the two officers had worked together only twice. Walsh, who testified at Van Dyke’s trial under a grant of immunity, backed up his partner’s claim that McDonald, holding a knife, was moving aggressively toward them when Van Dyke opened fire.

David March is a longtime CPD detective who led the investigation of the McDonald shooting, gathering statements from officers at the scene that night and signing off off on most of the reports in the case.

What are the charges?

The three are charged in a conspiracy to corrupt the investigation of the McDonald shooting, intending to protect Van Dyke, official misconduct and obstruction of justice.

What, allegedly, did they do?

The charges against the three officers largely hinge on reports they filed that indicated Van Dyke, Walsh and Gaffney were “victims” in a “battery” committed by McDonald. More specifically, the reports described aggressive acts allegedly taken by McDonald, including swinging a knife at the officers and later trying to get up after he was hit by gunshots that sent him slumping to the ground. However, video from a squad car at the scene shows there were no such aggressive actions by McDonald. In pre-trial hearings, lawyers for the three officers have seemingly argued that the CPD reporting software requires certain fields to be filled out — essentially forcing the officers to imply that they had been battered, and even injured, by McDonald.

Anything else?

A court filing outlining the evidence prosecutors intend to bring at trial fleshed out other details of how the officers allegedly coordinated their stories and mentions a number of unnamed police co-conspirators. Prosecutors allege Van Dyke and the other officers at the scene discussed the shooting together at Area Central headquarters before giving individual statements to March. At least one officer who was at the scene, Dora Fontaine, is expected to testify that March essentially coached her into giving a statement that described McDonald as the aggressor in the shooting.

Related: A look at the key players in the alleged cover-up of the MdDonald shooting

Prosecutors also have noted actions that would appear to show the department’s bias toward clearing Van Dyke in the shooting extended beyond the officers at the scene and March. The sergeant and the lieutenant who supervised March also apparently exchanged emails that allegedly mischaracterized the chain of events that led to the shooting, and suggested McDonald may have tried to commit “suicide by cop.” Months after the department closed its investigation, prosecutors said emails showed those senior officers were communicating with the union that represents CPD officers about helping Van Dyke’s legal defense and possibly gathered records of the investigation for the union.

What’s at stake for the officers?

Walsh and March both retired from CPD in 2016, after a city Inspector General report recommended they be fired. Gaffney remains on the force but has been on unpaid suspension since charges were announced. A conviction for official misconduct carries a penalty of up to five years in prison, while obstruction of justice carries up to three years. If acquitted, Gaffney could presumably keep his job — the IG report did not recommend firing him.

How long will the trial take?

Substantially less time than Van Dyke’s three-week trial. The three officers have opted for a bench trial in front of Judge Domenica Stephenson, and prosecutors have asked for a little more than two days to make their case.