Baltimore, Maryland (CNN)The first of six city police officers went on trial Monday in a closely watched case involving a 25-year-old black prisoner who died after being shackled and placed without a seat belt in a Baltimore City police van.

The April 19 death of Freddie Gray made him a symbol of the black community's distrust of police. His name is now invoked with those of Michael Brown in Ferguson, Missouri; Tamir Rice in Cleveland, Ohio; Eric Garner in New York; and other black men who died during encounters with white police officers. In Gray's case, three of the officers charged are white; three black.

On Monday, jury selection began in the trial of Officer William Porter, 26. Porter, who is black, is charged with manslaughter, assault and reckless endangerment. He has pleaded not guilty.

The first pool of potential jurors included about 75 people, some 40 of whom are African American. The others are white, with the exception of one Latino and one East Indian.

All of them told Judge Barry Williams they knew about Gray's death and about a financial settlement the city had reached with his family.

Inside the courtroom, the chants of protesters outside could be heard clearly: "All night, all day, we're going to fight for Freddie Gray."Following preliminary questions, potential jurors were individually questioned in a conference room out of view of reporters. About half of the potential jurors said they had been either the victim of a crime, investigated by law enforcement, convicted, incarcerated or were under pending criminal charges.

On Tuesday, a new pool of potential jurors will be brought into the courtroom for similar questioning. Some of those questioned Monday will be told they don't need to return; the remaining jurors from Monday will be asked to return on Wednesday.

Williams said opening statements and testimony would begin in the next few days and that the trial in Baltimore City Circuit Court would be over by December 17.Officials have said Gray ran from officers who were trying to arrest him on April 12. He was taken into custody near his home in a public housing project called Gilmor Homes, in the heart of a West Baltimore neighborhood called Sandtown-Winchester. The streets there are lined with boarded-up row houses.

Still to be answered is one of the most troubling questions in this case: How exactly was Gray injured? Was he the target of a "rough ride," a reputed police tactic reserved for particularly resistant suspects?

This much is certain: Gray was animated and angry before his arrest. As he was being transported in the police van, Gray complained of having trouble breathing and asked for medical help. He was unconscious when he arrived at the substation. And a week later, he died in a hospital.Although he is the first to go to trial, Porter isn't facing the most serious of the charges. Prosecutors have indicated in court filings that they consider Porter a potential witness against some of the other officers. If he is convicted, prosecutors could try to force his testimony in their trials.

Five of the six officers charged in Gray's death, including Porter, gave statements to investigators. They deny using force and have pleaded not guilty to charges ranging from official misconduct to second-degree murder with a depraved heart. The sixth suspect, the van driver, refused to talk with investigators.

Gray's death spawned protests that erupted on April 27 -- the day of his funeral -- into violent clashes with police and widespread looting and arson. Hundreds of people were arrested, more than 100 police officers were injured. City officials imposed a curfew, and the governor called in the National Guard to help restore order.Now, seven months later, the trials of the officers are beginning at a time of increased national focus on alleged mistreatment of young black men in police custody. Despite interest in the officers' trials, no cameras or electronic devices are permitted in the courtroom. No daily transcripts will be provided. And the lawyers on both sides are under a gag order.

All six officers are being tried separately and consecutively. Next up is the van driver, Caeser Goodson, whose trial is set to begin on January 6. Goodson, a black officer who is the lead defendant in the indictment, is charged with the most serious offense -- second-degree murder with a depraved heart.

Despite the strained atmosphere, which has led to protests outside the courthouse at some hearings, winning convictions won't be easy for prosecutors. Juries tend to be reluctant to convict police officers -- especially when the witnesses against them have criminal records.

Prosecutors face an even steeper uphill battle in Porter's trial: His alleged crime is one of inaction, of failing to heed Gray's pleas for medical help and failing to secure him inside the police van with a seat belt.

Porter did not witness Gray's arrest; he was called in as backup after Gray was in custody. He told investigators that he noticed the prisoner appeared to be in medical distress. The Baltimore Sun, relying on a source close to the investigation, has reported that Porter also told investigators that while he informed the van's driver, he also questioned whether Gray could be faking.Porter's lawyers have indicated in court documents that he will testify in his own defense, as will another prisoner who was with Gray in the police van.

At 25, Gray already had a lengthy rap sheet. Porter said in an interview with The Washington Post that Gray was known to officers as a "frequent flyer" with several arrests dating back to his teens. Most of them involve possession or sales of heroin and marijuana.

The city and police officials have acknowledged serious errors in the way Gray was handled in custody. In an unusual move, the city agreed to pay Gray's family $6.4 million to settle legal claims before the criminal trials began.