The Chicago Police Department says it is conducting "a very comprehensive review" after the city experienced one of its most violent Fourth of July weekends in recent years, with at least 102 people shot between late Friday afternoon and early Wednesday.



"We're doing a debriefing," said chief police spokesman Anthony Guglielmi. "The mood here is frustration."



The review will include an analysis of how "amateur fireworks" might have affected the ShotSpotter system, which captures audio of gunfire and attempts to pinpoint its location for quicker deployment of officers. The system is deployed in the Englewood and Harrison districts, traditionally among the city's most violent.



"It's perplexing," Guglielmi said. "We deployed some very successful tactics over the Memorial Day weekend." Yet those same tactics did not seem to work as well over the Fourth holiday.



Fifteen people were killed and 87 others were wounded. Nearly half the shootings occurred in the last 12 hours of the long holiday.



The last time the Fourth holiday spanned four full days was in 2013, when July 4 fell on a Thursday and many people had Friday off. At least 74 people were shot between Wednesday evening and early Monday that year, and 12 of them died, according to Tribune data.



The violence this year was largely confined to the South and West sides, where hundreds of officers on overtime were deployed. The youngest person shot was a 13-year-old boy seriously wounded in Gage Park on Friday night. The oldest was a 60-year-old man in the Lawndale neighborhood.



The weekend had been relatively calm when police Superintendent Eddie Johnson held a news conference early Tuesday afternoon and announced the arrests of 58 people on drug and gun charges "to keep residents and visitors safe in every neighborhood."



But within hours, violence erupted in nearly every police district south of North Avenue, according to data kept by the Tribune. At least 43 people were shot between 3:30 p.m. Tuesday and 3:30 a.m. Wednesday. Only two of those 43 were shot north of Chicago Avenue.



As part of its review of what happened over the weekend, the department is looking at how fireworks may have interfered with the ShotSpotter system, a relatively new technology the department hopes to expand.



The spotters register a shooting and deploy cameras in the direction of the shots while officers are deployed. Analysts at the district station look at the data in real time to decide what steps to take next. Guglielmi called it "micro-deployment."



The department is also reviewing calls for service, particularly as the weekend ended. "A lot of incidents happened in a short amount of time. We're also looking at that. We did typically see it (violence) where we typically see it."



A lot of the shootings appeared to be over "petty disputes that escalated into somebody pulling out a gun." He mentioned some examples: A shooting in Smith Park that started as an argument over where people were sitting; a confrontation between a driver and bicyclists on State Street, with the driver getting a gun from his trunk and officers intervening.



He said a "handful" of shootings were "retaliatory .. People drinking all day and then things escalating ... It's just enormously frustrating."



A total of 1,300 extra officers were deployed over the long weekend through 6 a.m. Wednesday. The additional officers came from the summer mobile teams, organized crime units and area saturation teams. "I don't think lack of resources was an issue."



A total of 159 guns were seized by Chicago police since Friday. "We have to change the underlying culture," Guglielmi said.



The weekend began with 19 people shot on Friday night and 23 on Saturday. Sunday and Monday nights were both relatively quiet, by summer standards, with 17 people shot over the two days, according to Tribune data.



The Harrison District on the West Side, which had gone without any shootings over the Memorial Day weekend, recorded 14 people shot over the long Fourth weekend.



At one homicide scene in the district, onlookers peeked around the entrance to the Green Line station at Pulaski Road and Lake Street, trying to get a glimpse of the body of a man chased down and shot early Wednesday.



The shooting happened on two sides of a popular West Side liquor store. Officers found shell casings and one man shot behind the store, next to an alley. The other wounded man fell face-up on a sidewalk underneath the elevated train tracks.



A garbage can fire burned as officers counted shell casings and draped tape from support pillars holding up the "L" tracks. A fire engine backed down the alley, and firefighters dumped the trash and pumped water from a tin can onto the smoldering waste.



Other scenes from the weekend



• The only shooting north of North Avenue happened about 50 yards from the street that marks the West Side's northern edge.



A 56-year-old man died and a 19-year-old man was seriously wounded around 8:15 p.m. Tuesday in the 1600 block of North Major Avenue -- the same block where an 8-year-old girl was shot last August. The house where the two men were shot was home to a young man killed last year around the corner. The older man was pronounced dead overnight at Loyola University Medical Center.



Tuesday night, a man approached the crime scene with a toddler, who seemed to be just learning to walk as she ambled ahead of him. An officer walked up to the little girl and gently turned her around, while another yelled at her father for walking under yellow tape officers had stretched across Major Avenue.



• Seven miles to the south, shortly before midnight, a woman searched the 1900 block of South Spaulding for shell casings by the light of her cellphone before officers arrived. Two people walked into St. Anthony's Hospital, a block from Mount Sinai Hospital, saying they had been shot there.



• Earlier Tuesday, officers found a woman shot on Roosevelt Road. She was in a silver car just east of Independence Boulevard and had been shot around the corner, on Lawndale Avenue. Every few minutes, officers found a few more shell casings, each a little farther from the alley south of Roosevelt.



• Police found a 42-year-old man in "extremely critical" condition on Laflin Street just south of 62nd Street, and he was later pronounced dead from gunshot wounds. Neighbors gathered on a front porch nearby and in a smaller group across the street, on church steps, while paramedics worked on the man. The ambulance left after a few minutes with a squad car in tow.



• Just before 3 a.m. Wednesday, police taped off Roosevelt Road because they found a person shot where the road intersects with Loomis Avenue in the University Village/Little Italy neighborhood. He had been shot about a block south on the 1300 block of West 13th Street.



• A shooting in the 3400 block of West Grenshaw Street about 10:15 p.m. left two men wounded. People nearby said they hesitated when they heard the gunfire but weren't certain because of the frequency of the fireworks. A woman, who neighbors said was the young man's grandmother, stepped to the ambulance to find out what happened.



"Right now, ma'am, he's worried about you. He's going to be OK, but he's worried about you," a paramedic told the woman. She stepped away, and the ambulance pulled off toward Mount Sinai Hospital.



"I can't go with him?" she asked.



Mount Sinai Hospital treated at least 22 of the 102 people shot over the weekend. At one point early Wednesday morning, five ambulances crowded into the emergency room's small ambulance bay and a Chicago police squad SUV sat parked nearby.