CHICAGO (CBS) — Jury selection begins Friday in the trial of two men charged in one of Chicago’s most horrific crimes, the execution-style killing of 9-year-old Tyshawn Lee in an act of revenge in 2015.

“It was the worst form of evil I think I’ve ever seen,” said Rev. Michael Pfleger, who presided over Tyshawn’s funeral.

Pfleger said the details of Tyshawn’s murder were a new low for Chicago.

A basketball was laying just a few feet from Tyshawn’s lifeless body, when he was found dead in an alley on Nov. 2, 2015.

“He had this amazing smile and laughter,” Pfleger said. “He loved basketball. His dream was to be an NBA player.”

Tyshawn Lee (Photo supplied to CBS)

Police and prosecutors have said 26-year-old Kevin Edwards, 31-year-old Corey Morgan, and 25-year-old Dwright Boone-Doty targeted Tyshawn in retaliation for the gang-killing of Morgan’s brother, Tracy Morgan, who was gunned down three weeks before Tyshawn was slain. Tyshawn’s father was a member of a rival gang suspected of shooting Morgan’s brother.

“I think sometimes we just try to almost block it out because it’s so painful to remember and to think about it,” Pfleger said.

Police and prosecutors said both shootings stemmed from an ongoing gang war between the Terror Dome faction of the Black P-Stones and the Killa Ward faction of the Gangster Disciples.

Dwright Boone-Doty (left), Corey Morgan (center), and Kevin Edwards (right) are charged with first-degree murder in the execution-style shooting of 9-year-old Tyshawn Lee. (Source: Cook County Sheriff)

Morgan, Boone-Doty, and Edwards allegedly spotted Tyshawn playing basketball at Dawes Park at 80th and Damen on Nov. 2, 2015. Morgan and Edwards drove off in an SUV while Boone-Doty stayed behind.

Tyshawn put down his basketball and began playing on the swings at the park, and Boone-Doty walked up to him and offered to take him to the store and buy him anything he wanted, prosecutors said. Boone-Doty then allegedly lured Tyshawn into a nearby alley with the promise of a juice box.

Once they got to the alley, Boone-Doty he allegedly shot Tyshawn multiple times at close range.

Edwards then drove Morgan and Boone-Doty away from the scene.

“This was a targeted assassination,” acting Chicago Police Supt. John Escalante said at the time. “These are calculated killers whose actions define the words brutality and cowardice.”

Morgan and Boone-Doty were arrested about two weeks after Tyshawn was killed. Edwards was arrested six months later in downstate Danville.

Edwards has pleaded guilty to first-degree murder in exchange for a 25-year sentence.

Morgan and Boone-Doty are scheduled to go on trial in the case. Separate juries will decide each man’s fate, with Boone-Doty’s jury selection starting Friday and Morgan’s jury selection scheduled for Monday.

Authorities have said Boone-Doty admitted his role in Tyshawn’s death and said when he shot the boy, he “seen that bitch go in his head.”

Pfleger said Tyshawn’s death left a horrible scar within the community.

“One of his classmates ended up having to go to a mental institution a few weeks later because of the trauma,” Pfleger said.

Tyshawn Lee, 9, was fatally shot in the Gresham neighborhood. (Courtesy: Karla Lee)

The pastor said that’s why the trial is so important.

“People have to be accountable. When you shoot and kill, you gotta go to prison,” he said.

Police have said they couldn’t believe what detectives learned as they investigated Tyshawn’s murder; from a rap song Boone-Doty allegedly wrote about the shooting, to his jokingly referring to Tyshawn as “Shorty” when he allegedly told friends what had happened: “Shorty couldn’t take it no more.”

“This was something we didn’t even think humanly possible for even hardened gang members,” said John Escalante, who was the interim police superintendent when Boone-Doty was charged four months after the attack and who has since left the department.

On the day Boone-Doty first appeared in court accused of killing Tyshawn, the boy’s father, Pierre Stokes, allegedly opened fire on gang rivals, wounding three of them, authorities have said. Stokes is in jail awaiting trial on aggravated battery and other charges in that attack.