FERGUSON, Mo. (AP) _ After an unarmed black teenager was shot by a Ferguson, Missouri, police officer, authorities have resisted calls to release the name of the officer while imploring protesters to keep their demonstrations calm and avoid new trouble in the city north of downtown St. Louis. Here’s a look at the key elements of the shooting and the unrest that followed:

THE SHOOTING: Police have said the shooting happened after an officer encountered 18-year-old Michael Brown and another man on the street. They say one of the men pushed the officer into his squad car, then physically assaulted him in the vehicle and struggled with the officer over the officer’s weapon. At least one shot was fired inside the car. The struggle then spilled onto the street, where Brown was shot multiple times. Dorian Johnson, who says he was with Brown when the shooting happened, has told a much different story. He has told media outlets that the officer ordered them out of the street, then tried to open his door so close to the men that it “ricocheted” back, apparently upsetting the officer. Johnson says the officer grabbed his friend’s neck, then tried to pull him into the car before brandishing his weapon and firing. He says Brown started to run and the officer pursued him, firing multiple times. Johnson and another witness both say Brown was on the street with his hands raised when the officer fired at him repeatedly.

THE UNREST: Ferguson city leaders on Wednesday asked angry residents to keep their protests peaceful and to end them before nightfall in an effort minimize trouble. Early Wednesday, a St. Louis County police officer shot and wounded a man who authorities said pulled a handgun on the officer. On previous nights, crowds have gathered to protest Brown’s death, and residents were seen looting stores, damaging buildings and vandalizing property. On Monday night, police used tear gas and fired “bean bag” rounds after a crowd turned rowdy, throwing rocks and bottles at officers. More than three dozen people have been arrested. Brown’s family and civil-rights groups have pleaded for the community to stay calm.

THE INVESTIGATION: Brown’s death is being investigated by St. Louis County police at the request of the smaller police department in Ferguson. The FBI has also opened an investigation into possible civil rights violations. Authorities are refusing to release any details about their investigation or identify the police officer who shot Brown. Ferguson police say releasing the officer’s name will lead to retribution, while protesters and attorneys for Brown’s family say knowing who pulled the trigger will help the community heal and determine if the officer may have been involved in previous incidents. The Justice Department has sent community relations experts to help Ferguson officers address their community’s mistrust of the police.

THE PUBLIC DISCUSSION: Some civil rights leaders have drawn comparisons between Brown’s death and that of 17-year-old Trayvon Martin, who was fatally shot by a Florida neighborhood watch organizer who was later acquitted of murder charges. The St. Louis case provoked a broad discussion on social media sites about the death of young black men in racially tinged shootings. On Twitter, a campaign using the hashtag (hash)IfTheyGunnedMeDown has prompted many black users to post photos of themselves and ask how they might be portrayed in news reports if they became shooting victims.