Bryon Champ decided to seek quick revenge last week after he was grazed in the leg in a gang-related shooting, authorities say.

The convicted felon reached out to Kewane Gatewood, who for a few months had been hiding an AK-47-style rifle under his bed for Champ, according to authorities.

Just hours after he had been injured, Champ and Tabari Young, one armed with the assault rifle and the other toting a .22-caliber handgun, indiscriminately opened fire Thursday night at a crowded South Side park that they considered the turf of the rival gang, police and prosecutors alleged.

In one of Chicago's most chilling mass shootings in recent history, a 3-year-old boy and a dozen others enjoying a warm evening in the waning days of summer lay wounded in Cornell Square Park in the Back of the Yards neighborhood.

Five days after the bloodshed, police and prosecutors on Tuesday laid out their narrative for how a seemingly petty gang dispute again painted the city as gripped by gun violence. What stood out about the attack as well was the use of a military-grade weapon, highly unusual for gang warfare in impoverished pockets of the South and West sides.

Champ, 21; Young, 22; Gatewood, 20; and Brad Jett, 22, an alleged lookout at the shooting scene, were all ordered held without bond on three counts each of attempted murder and aggravated battery with a firearm.

At a news conference announcing the overnight charges against the two gunmen, police Superintendent Garry McCarthy decried a boot camp sentence given to Champ last year for a weapons offense, saying if he had been appropriately punished, the mass shooting likely would not have happened.

"Illegal guns drive violence," said McCarthy, driving home a point he has been making for months. "If we don't provide real punishment for the criminals who carry them, what message is it that we're sending? Where are the priorities of the criminal justice system?"

Appearing before reporters outside Mount Sinai Children's Hospital on Tuesday night, the mother of the shooting's youngest victim, 3-year-old Deonta Howard, mustered some compassion for the men charged.

"I can't hold no grudges against them," said Shamarah Leggett, 24, whose son was shot in the face. "I am glad justice has been served. All I can do is pray for them. They are young men. All I can do is pray."

At a bond hearing in the Leighton Criminal Court Building, Assistant State's Attorney John Dillon identified Champ as a Black P Stones gang member who had suffered a graze wound to his leg in a shooting involving Gangster Disciples hours before the mayhem in the park.

After hearing from Champ, Gatewood delivered the AK-47 to a "stash house" where Champ hung out, according to Dillon. The prosecutor alleged that Gatewood knew Champ planned to use the high-powered weapon in retaliation for the earlier shooting.

Jett and another offender who hasn't been charged went looking for rival Gangster Disciples and found them at Cornell Square Park near Wood and 50th Streets, Dillon said. As Jett acted as a lookout by a gangway, Champ and Young opened fire at about 10:15 p.m., according to Dillon, as many of the victims played on a basketball court.

All four defendants admitted to their roles in the shooting, Dillon said.

But there appeared to be some confusion over who wielded the AK-47. McCarthy said Young fired the weapon, but prosecutors later said Champ had used the rifle. Later, a prosecutor source said the two suspects had fingered each other as the one who fired the powerful weapon.

Assistant Public Defender Anand Sundaram, who represented all four defendants at the bond hearing, later attacked the strength of the prosecution evidence and noted that police had not recovered any of the weapons used in the shooting. He also pointed to the confusion over who used the AK-47 and questioned the accounts of eyewitnesses given the chaotic scene in the park.

"When shots are fired, people run around so it would be hard to imagine a good ID in that case," Sundaram told reporters.

Relatives of Champ and Jett who attended the bond hearing declined to comment to reporters.

Court and police records show Champ pleaded guilty in February 2010 to felony possession of a stolen motor vehicle and was sentenced to 18 months of probation. After he was arrested in May 2011 on a felony drug charge, he also was charged with violating probation and held in jail for 22 days. The drug charge was later dropped.

Then in June 2012, police heard gun shots near 53rd Street and Marshfield Avenue and saw a man wielding a handgun run into an apartment building. They arrested Champ and found a loaded 40-caliber Smith and Wesson, records show. He pleaded guilty the next month to felony aggravated unlawful use of a weapon by a felon and was sentenced to boot camp.

Young has more than a dozen arrests for mostly minor marijuana possession charges that were later dropped. His only conviction appears to be a misdemeanor criminal trespass to a vehicle; he was sentenced to four days he had already served in jail.

Young's brother, Devon, was fatally shot by Chicago police in June 2008, according to his family and records.

Jett was arrested in March 2010 on a felony drug possession charge and then while out on bond picked up a crack-cocaine possession charge the following October, records show. He pleaded guilty to both charges and was sentenced to 24 months probation. Last September he was arrested on a probation violation and jailed until November.

Gatewood, who has no criminal background, is currently enrolled as a culinary student at Kennedy-King College, the school confirmed.

The arrest stunned his mother, who held back tears during an interview Tuesday outside her home.

"Half of me is gone," said Jacqueline Irvin, who indicated her son has been cooking the family Thanksgiving and Christmas dinners since elementary school.

She said Gatewood was home with her Thursday night playing video games. The two had talked briefly Tuesday, she said.

"(He's) very scared because it's something new for him," she said.

Tribune reporters Rosemary Regina Sobol, Carlos Sadovi, Liam Ford, Steve Schmadeke and Lauren Zumbach contributed.

jgorner@tribune.com

lbowean@tribune.com