CHICAGO (CBS)—The shootings that gripped Chicago over the weekend were shocking, even by Chicago’s standards.

By Monday morning, 12 people were killed and 54 were wounded in shootings across four neighborhoods on the city’s south and west sides.

The weekend of August 4-5 was one of Chicago’s most violent periods in recent history, yet police admitted no arrests had been made in the wake of the violence.

The shootings shook up the city, from the family members and friends of the victims, to Mayor Rahm Emanuel, who grappled with a response to the violence during a joint press-conference with Police Supt. Eddie Johnson Monday morning.

Emanuel said there was a shortage of values among the people responsible for the killings.

“We have a heavy heart,” Emanuel said. “Our souls are burdened. What happened this weekend did not happen in every neighborhood in Chicago, but it is unacceptable to happen in any weekend in Chicago.”

The alarming number of shootings grabbed nationwide headlines, with former New York City Mayor Rudy Giuliani tweeting about Chicago violence on Twitter.

Johnson blamed the bloody weekend on the offenders.

“It’s the psychology of the people pulling these triggers,” Johnson said.

Anti-crime activist Camiella Williams says she’s lost 30 people she knows to violence. She told CBS 2’s Roseanne Tellez that the killers lack coping skills.

“This is about disrespect—power,” Williams said. “If you live in a certain community and they know that and you cross into their community it makes you an automatic target.”

Johnson called on everyone to do their part to stop the violence. He said someone knows what happened and he called on the public to report the shooters.

“Someone knows who did it,” Johnson said.

Among the victims who died are a teenager who was trying to get his bike back from thieves and an aspiring lawyer.

CBS 2’s Suzanne Le Mignot met with longtime Lawndale resident Gloria Muldrow, who said she’s constantly preoccupied with worries about her family.

Muldrow–who lives four blocks away from 15th Street and Avers where four people were shot over the weekend– remembers the days when there were no drive-by shootings and boarded up homes along her street.

Muldrow, a grandmother, says a simple walk to the store or a visit to the local park isn’t an option for her family anymore.

“We should be able to walk free and go where we want to go, but we can’t do that now,” Muldrow said. “I feel like our lives should be like the north side people’s lives–we should be at peace.

She spoke to Le Mignot from her porch step Monday, but said she usually doesn’t let her family sit outside.

“There’s too much violence and you don’t know which way the bullets are going to come from,” she said.

Why the spike in violence now? Why this weekend as opposed to other summer weekends?  CBS 2’s Dana Kozlov delves into that part of the story.

Sharon Homan co-directs the Gun Violence Research Collaborative, a group that’s spent two years trying to find root causes of violence and solutions to violence in neighborhoods hit the hardest.

“I think it plays a ton, but it isn’t the only source,” Homan said, referring to gang violence and gang affiliations.

Homan cites the “pure availability of guns” as perhaps the biggest factor. She acknowledges it is a complex problem as concerns are echoed by many city leaders.

CBS 2’s Roseanne Tellez, Suzanne LeMignot, and Dana Kozlov contributed to this story. 

See CBS 2’s coverage of the shootings here: 

At Least 30 People Shot Overnight In Chicago 

‘We Have A Heavy Heart’: Mayor, Top Cop Lament Bloody Weekend In Chicago

Giuliani Praises ‘Jerry’ McCarthy, Slams Rahm ‘Emmanuel’ In Tweetstorm On Chicago Gun Violence

List Of The Dead In Weekend Of Chicago Violence