Chicago experienced a violent Fourth of July holiday weekend, with more than 100 people shot between late Friday (30 June) and early Wednesday (5 July).
Chicago Police said it is conducting a "very comprehensive review" following the particularly brutal weekend.
"We're doing a debriefing," chief police spokesman Anthony Guglielmi told the Chicago Tribune. "The mood here is frustration," he added.
Nearly half of the shootings over the holiday weekend occurred over 12 hours on Tuesday (4 July) and Wednesday in the city's South and West sides, the Tribune reported. Hundreds of officers on overtime were deployed to those areas.
According to the Tribune, 15 people were killed and 86 more were injured. The youngest victim was a 13-year-old boy in Gage Park on Friday, while the oldest was reportedly a 60-year-old man in the Lawndale neighbourhood.
The four-day weekend was the longest since 2013, when 4 July fell on a Thursday. Tribune data revealed that at least 74 people were shot that year, with 12 people dying.
The review conducted by authorities will include an analysis of how "amateur fireworks" may have affected the department's ShotSpotter system, which captures the sound of gunfire and tries to pinpoint its location to quickly deploy officers. The Tribune reported the system is used in the Englewood and Harrison districts, which are among Chicago's most violent.
"It's perplexing," Guglielmi said. "We deployed some very successful tactics over the Memorial Day weekend." Those tactics did not appeared to work over the Fourth holiday.
On Tuesday, police Superintendent Eddie Johnson announced that 58 people had been arrested on drug and gun charges "to keep residents and visitors safe in every neighbourhood". Within hours of the news conference, violence reportedly sprouted in nearly all police districts south of North Avenue.
"A lot of incidents happened in a short amount of time," Guglielmi said. "We're also looking at that. We did typically see it (violence) where we typically see it." He said that many of the shootings appeared to be over "petty disputes that escalated into somebody pulling out a gun".
Guglielmi said that 1,300 additional officers were deployed over the long weekend through 6am Wednesday. Those officers came from the summer mobile teams, organised crime units and area saturation teams. "I don't think lack of resources was an issue," he said.
Chicago Police seized a total of 159 guns since Friday.