The Washington Post's Wesley Lowery and social media users captured video of protests and clashes with police in Ferguson, Mo., on Tuesday. It was the third day of rallies for Michael Brown, an unarmed teen fatally shot by a police officer on Saturday. (Sarah Parnass and Wesley Lowery/The Washington Post)

The Washington Post's Wesley Lowery and social media users captured video of protests and clashes with police in Ferguson, Mo., on Tuesday. It was the third day of rallies for Michael Brown, an unarmed teen fatally shot by a police officer on Saturday. (Sarah Parnass and Wesley Lowery/The Washington Post)

When an unarmed black teenager and a police officer crossed paths here last weekend with fatal results, the incident cast a blinding spotlight on a small police department struggling for authority and relevance in a changing community.

Since the shooting, the department has been criticized for how police have handled the response to the incident and for not disclosing key details, including the name of the officer involved.

The department bears little demographic resemblance to the citizens of this St. Louis suburb, a mostly African American community whose suspicions of the law enforcement agency preceded Saturday afternoon’s shooting of Michael Brown, an 18-year-old who this week had been headed to technical college.

But while the racial disparity between the public here and its protectors has come to define the violent aftermath of Brown’s death, the department’s problems stretch back years and include questions about its officers’ training and racial sensitivity.

The office of Missouri’s attorney general concluded in an annual report last year that Ferguson police were twice as likely to arrest African Americans during traffic stops as they were whites.

And late last year, the state chapter of the NAACP filed a federal complaint against the St. Louis County police department, whose officers are now assisting Ferguson’s force since the shooting, over racial disparities in traffic stops, arrests and other actions.

Tensions between residents and the police have shaped the aftermath of Brown’s death in unpredictable and alarming ways. Those include the nightly clashes between young residents, most of whom are African American, and a predominantly white police force dressed in full riot gear and armed with tear gas and rubber-coated bullets.

Early Wednesday morning, a St. Louis County police officer shot and critically wounded a man who pointed a gun at the officer, a police spokesman said. Police had responded to calls regarding four men armed with shotguns and wearing ski masks in St. Louis as well as calls about shots fired in the area. People fled the scene when police arrived, but one person pointed a handgun at an officer, who shot the man, spokesman Brian Schellman said.

Police officials have provided little information about Brown’s shooting and have withheld the name of the police officer involved, citing security reasons. The vacuum has been filled by social media, which has displayed in real time street confrontations between police and demonstrators, documenting the fraught interactions in images, videos and short dispatches.

On Wednesday, Ferguson Police Chief Thomas Jackson acknowledged the problems facing his department and asked the community for help in restoring its trust.

“Apparently, there has been this undertow that has bubbled to the surface,” Jackson said at a news conference. “It’s our priority to address it and to fix what’s been going wrong.”

St. Louis is among the most segregated metropolitan areas in the nation. Ferguson, one of the 91 municipalities in largely white St. Louis County, has seen its population shift in recent years. About two-thirds of the city’s 21,100 residents are black. That’s a significant increase from 2000, when blacks made up just over half of the population. White residents, who had accounted for 44 percent of the population, now make up just under 30 percent.

1 of 62 Full Screen Autoplay Close Aug. 11, 2014 Aug. 10, 2014 Sunday Aug. 9, 2014 Saturday Skip Ad × Protests continue after killing of Missouri teen by police View Photos Demonstrations, social media and talk shows swirled with anger aimed at both Michael Brown’s death and the violent protests that followed the shooting of the unarmed teen Saturday night. Caption Demonstrations, social media and talk shows swirled with anger aimed at both Michael Brown’s death and the violent protests that followed the shooting of the unarmed teen Saturday night Aug. 12, 2014 Demonstrators outside St. Louis County Circuit Court building in Clayton, Mo., raise their hands while protesting the shooting death of black teenager Michael Brown on Saturday night in Ferguson. Mario Anzuoni/Reuters Buy Photo Wait 1 second to continue.

Yet the police force patrolling Ferguson has not changed along with the population. The police force has 53 members, and three of them are black. The city’s mayor and police chief are white, as are most of the members of the Ferguson City Council.

“I’ve been trying to increase the diversity of the department ever since I got here,” Jackson said Wednesday. He pointed out that he had promoted two black superintendents.

“Race relations is a top priority right now,” Jackson said. He said his force is working with the Department of Justice’s community relations office to improve how police interact with the citizens. “I’ve told them, ‘Tell me what to do, and I’ll do it.’ ”

Residents have described Brown’s death as a breaking point that finally pushed years of tension to the fore.

“People here are angry, frustrated,” said Corey Crawford, 36. “There needs to be justice. If you can find a single person in this community who trusts the police, that is like finding a four-leafed clover.”

It has been “very hostile” for years, said Anthony Ross, 26, who lives nearby. He called the relationship between residents and police nonexistent.

“Everybody in this city has been a victim of DWB [driving while black],” he said.

For at least a decade, there have been complaints about racial tensions between police and black communities in the St. Louis County area. Communities, some residents say, can have less-experienced, poorly-equipped police departments and highly uneven levels of protection.

This year, St. Louis County invited researchers from the University of California at Los Angeles to help study complaints that county police had engaged in racial profiling and to help them improve protocols for matters ranging from traffic stops to neighborhood monitoring.

This came after a former lieutenant with the county police who had been accused of ordering officers to target black people at stores was fired. An investigation determined that he had made “inappropriate racial references.”

A St. Louis Post-Dispatch investigation in 2003 found that dozens of small police departments in the region suffered from poor training owing to a lack of funding, leading to inadequate investigations of complex crimes and an uneven use of force. The newspaper further found that this led to problematic officers moving easily between one city’s force to another without punishment.

As attention has shifted to the protests and nightly standoffs on Ferguson’s streets, key details regarding the shooting remain unclear. Authorities have yet to say how many times Brown was shot or where he was struck. Earlier in the week, St. Louis County Police Chief Jon Belmar said that Brown was shot multiple times but did not elaborate.

But on Wednesday, Jackson, Ferguson’s police chief, would not say how many times Brown was shot. The only update regarding the confrontation came Wednesday, when Jackson said that the officer’s “face was swollen” after the encounter, so he required medical treatment. Police have said that Brown was shot after a physical confrontation with the officer, including a struggle over the officer’s gun, which witnesses have disputed.

During a separate news conference Wednesday, Robert P. McCulloch, the St. Louis County prosecuting attorney, also declined to say how many times Brown was shot.

“We want to test the veracity and accuracy of anybody who comes to us with a statement and says they saw something,” McCulloch said.

Jackson said in an interview Wednesday that he was driving with his children to lunch Saturday when a sergeant called him about the shooting. Before even arriving at the scene, Jackson called county police to take over the investigation.

But as protesters from the community and neighboring city flooded Ferguson’s streets for both prayer vigils and tense standoffs, Ferguson again called on the county for help. Hundreds of officers from St. Louis County police, the city of St. Louis and the Missouri State Highway Patrol arrived to help deal with the looting that had broken out.

In audio recordings released Wednesday by the hacking collective Anonymous, a voice identified as belonging to a county police dispatcher indicated that Ferguson police were unaware that one of their officers had been involved in Saturday’s shooting.

The female dispatcher noted that she had received two calls about an “officer-related shooting” on Canfield Drive.

“We just got another call about an officer-involved shooting . . . there,” she said. “This came from the news, so [unintelligible] don’t know.”

A few seconds later, the dispatcher, apparently frustrated that the information appeared to be coming from news accounts, said she couldn’t get confirmation from the police in Ferguson.

“We just called Ferguson back again, and they don’t know anything about it,” she said.

County police did not respond to a request for comment regarding the dispatch tape’s veracity.

Anonymous became widely known for its cyberattacks on government Web sites and credit card companies.

Julie Tate contributed to this story. Leonnig and Berman reported from Washington.