Tyshawn Lee's brutal murder has been an ongoing priority for Chicago Police who have made an arrest three weeks after the 9-year-old's death, The Chicago Sun Times reported. Corey Morgan is in custody on afirst-degree murder charge and is one of at least three people authorities have linked to Lee's murder.

Police Superintendent Garry McCarthy identified Morgan, and a second man in custody on unrelated charges. A third individual is at large, and all three are connected to the execution style slaying of the 9-year-old Tyshawn.

"This is a crime that shook our city," McCarthy said, according to CNN. "It was an act of barbarism, the assassination of a 9-year-old child as a gang retaliation to get back at his father. Tyshawn Lee was failed on many, many levels."

Gangs battle over turf and the right to sell drugs in what's known as the most dangerous neighborhood, Auburn-Gresham, where Tyshawn resided and was gunned down.

Deronce Curd, a longtime resident of Auburn-Gresham, is struggling to come to grips with the thought of gangs killing kids.

"How can a little boy, 9 years old, defend himself?" Curd asked. "This is just -- I'm speechless to what is going on right now."

With recent rival gang shootings, police believe that Tyshawn was lured into the alley and executed due to his father Pierre Stokes' gang ties. Morgan's brother Tracey was gunned down just three weeks prior to Tyshawn's murder, leading police to say that Tyshawn was targeted for retaliation for Tracey Morgan's death, according to CBS News. The Morgans' mother was also shot in the arm during the attack.

McCarthy called Tyshawn's murder "probably the most abhorrent, cowardly, unfathomable crime" seen in his 35 years of law enforcement.