(CNN) — Murder charges have been filed against a second suspect in the November 2015 killing of a 9-year-old boy, a crime that horrified a Chicago community.

Gang members targeted the boy, Tyshawn Lee, as part of a gang war, Chicago police have said. Tyshawn was lured into an alley and shot to death.

Prosecutors have charged Dwright Boone-Doty, 22, with first-degree murder in Tyshawn’s death, Chicago police spokesman Anthony Guglielmi told CNN.

Boone-Doty is already imprisoned on unrelated criminal charges. A multi-agency investigation, including a corrections intelligence team, uncovered evidence to charge the inmate with targeting, luring and executing the 9-year-old boy, Guglielmi said.

The Cook County State Attorney’s Office is expected to announce additional details at a Tuesday afternoon news conference.

Boone-Doty is the second person charged in Tyshawn’s killing. In November, Corey Morgan, 27, was arrested and charged with first-degree murder. At the time, police said Morgan didn’t act alone, but with two others, including one who was in custody on an unrelated charge. Boone-Doty is the suspect police were referring to.

The third suspect, Kevin Edwards, remains at large, Guglielmi said.

Court papers provided by the prosecutor’s office said that “Tyshawn’s death is the result of a gang war” between two particular gangs that “came to a boil” after Morgan’s brother, Tracy, was shot and killed in a car with their mother on October 13.

The mother was shot and wounded, court papers said.

“Shortly after the shooting [Corey Morgan] stated that since his brother was killed and his mama was shot he was going to kill grandmas, mamas, kids and all,” according to court documents.

An autopsy of Tyshawn’s body showed two perforating gunshot wounds, and part of his right thumb was lost as a defensive wound trying to block a gunshot, court papers said. The boy’s body had a gunshot wound to the head, a bullet graze wound to his right upper back, and a superficial wound to the right forearm, documents said.

“There was evidence of close-range firing,” court papers said.