The sun went down on a hot July evening and police noticed trouble brewing in South Baltimore.

Teens and young adults had converged on the annual block party at Brooklyn Homes. News of the party swept across the social media pages of Baltimore youth.

Officers radioed that the crowd had swelled to hundreds of people. Police dispatched a helicopter. By 10 p.m., someone posted online a video clip of a young man flashing what appeared to be a gun.

This scene wasn’t supposed to happen. The city has a network of offices and programs, even a curfew, intended to keep youth safe at night this summer.

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Eleven days have passed since the ensuing shooting killed two people and wounded 28 others — likely the worst mass shooting in Baltimore history — and questions linger.

Why didn’t police step in sooner? How could city leaders be unprepared for a party that happens every year? What went wrong?

City Council members will have a chance for answers during a public hearing Thursday to examine the failures of communication and action. Councilman Mark Conway, chairman of the committee for public safety and government operations, asked leaders from the Police Department, Housing Authority of Baltimore City, mayor’s office and Department of Transportation to attend. The hearing will be shown live online at 5 p.m.

“I want to understand what went wrong on the front end in preparation for the event. The Police Department did not know about it. Why not? Did any other agencies know about it?” Conway said. “Once we did know about it, we didn’t act. There seems to have been a number of calls about fights and guns and even a shooting.

“I would like to be able to walk away,” Conway said, “with a clear sense of what we need to do to be that much more prepared so nothing like this ever happens again.”

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Acting Police Commissioner Richard Worley said the department is reviewing its response to the shooting, gathering “every piece of data that we have: radio transmission, cell phones, text messages. Everything that we had to see who knew, what they did once they found out, and what was done, what was the result of what they’ve done,” he said in an interview Wednesday.

The department hopes to complete its review in 30 days. Worley said the findings could result in disciplinary actions.

Police have announced no arrests in the killings of Kylis Fagbemi, 20, and Aaliyah Gonzalez, 18. Mourners gathered Tuesday for a candlelight vigil to remember Fagbemi. Gonzalez had graduated this year from Glen Burnie High School. The wounded include boys and girls as young as 13. Authorities are offering $28,000 for information leading to arrests.

Last week, police arrested a 17-year-old on gun charges. A video clip from the party circulated widely online showed a young man flashing what appeared to be a gun. The attorney of the teen arrested, Michael Clinkscale, said the gun was just a toy. It’s the only arrest police announced and officers have not charged the teen with shooting anyone.

With hundreds of people around and shell casings tracing to more than a dozen guns, the investigation presents obvious difficulties.

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Police have offered no explanation for what caused the shooting; it’s unclear if detectives even know. Senate President Bill Ferguson said on WBAL radio that he watched video of the shooting. Ferguson was asked if the scene appeared to be warring gangs.

“I almost wish it were gangs. It would make it easier, because it would be a clearer explanation for what happened,” he said. “What I saw on the video was not orchestrated, planned out, coordinated, organized. It was total chaos. It was too many individuals with guns, or what appeared to be backpacks containing guns, and people got scared and all of a sudden, those particularly, I presume, younger people who had guns in their possession, started shooting.”

In his public remarks, Mayor Brandon Scott has blamed “cowardly” gunmen, the proliferation of firearms on the streets, and the inaction of Congress to keep guns out of the hands of children. He’s been less outspoken about the failures of city government to make sure the “Brooklyn Day” party proceeded safely, or for the hesitation of police to step in when the party was spiraling out of control.

Two women who attended the party said the crowd scattered repeatedly because of fears that someone had a gun. The DJ warned partygoers that this was no place for quarrels. Later, after midnight, the shooting started.

The city police union, Baltimore City Lodge No. 3 Fraternal Order of Police, seized on the violence to again draw attention to Baltimore’s persistent shortage of officers.

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“Would anyone care to guess how many officers from the patrol shift were working in the Southern District at the time of this mass shooting? SEVEN (7)! Ten years ago, there would have been 20 from the shift,” union leaders wrote on Twitter.

Worley said the union wasn’t entirely correct. “There were more than seven. Wasn’t much more, but there were more than seven.”

Shadowing the conversation about the city’s action — or apparent inaction — are questions about the mayor’s curfew. The curfew does not prohibit children from being outside at night when they are near home or with a guardian. Scott has said the curfew didn’t apply because the crowd included adults and children from the Brooklyn neighborhood. Indeed, the 17-year-old who was arrested lives nearby, his lawyer said.

Social media videos from that night, however, also show that Instagram posts led young people to the party from outside Brooklyn Homes and even outside the city. There are discrepancies between the mayor’s explanation and what’s understood about the party, Conway acknowledged. He expects the curfew to be discussed at the hearing.

“I’m not totally satisfied by that [the mayor’s] answer,” he said. “I’m not sure others are as well.”

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Four Safe Streets violence interrupters had monitored the party into the night and stepped in to calm some minor arguments. But their shifts went from 3 to 11 p.m. — the shooting started after midnight. The Brooklyn Safe Streets office is understaffed with two of the five positions currently open, according to the nonprofit that operates the site.

Community organizers also did not obtain a permit for the party and city leaders have pointed to this misstep as reason officials were not fully aware and prepared. A permit would have been issued by the Department of Transportation.

One of Scott’s key initiatives has been the Mayor’s Office of Neighborhood Safety and Engagement. In three years, the office has grown to include more than 30 staffers and a $22 million budget. It’s responsible for coordinating violence intervention work and overseeing programs such as Safe Streets. But the office was also caught unprepared; it’s unclear when or even if officials knew of the party.

“Sunday’s mass shooting is prompting an extensive assessment of every single aspect of what went wrong and what we need to do to fix it, from BPD’s response — which Acting Commissioner Worley has noted repeatedly — to MONSE and our violence interrupters. We are examining steps city agencies and partners take before and after incidents of violence,” the mayor said in a statement last week.

Baltimore was hardly alone in suffering gun violence around the Fourth of July. A block party in Salisbury also erupted with gunfire in the early morning hours of July 5. The shooting left a 14-year-old boy dead and six others wounded. Two men and two teenage boys were wounded during a shooting in Edgewood in Harford County.

Four people were killed and as many as seven others injured during a shooting at a July Fourth party in Shreveport, Louisiana. The night prior to that, three people were killed and eight others injured during a shooting at an outdoor party in Fort Worth, Texas. An analysis by CNN finds the July Fourth holiday and July 5 have more mass shootings than any other calendar dates.

Reporters Justin Fenton, Brenna Smith and Hallie Miller contributed to this story.