Willis, 33, had suspected Jonathan Watkins, 29, of stealing the video game system from his mother's home. On March 11, he opened fired as Watkins and his baby daughter sat parked in a minivan in the Woodlawn neighborhood. A bullet entered Jonylah's right shoulder and traveled down through her left thigh. She died the following day. Her father survived multiple gunshot wounds.

Kent said Watkins was in the front passenger seat of his van, changing his daughter’s diaper, at the time of the shooting. “Jonathan lifted Jonylah up to kiss her when the defendant approached and fired multiple gunshots into the van,” Kent said.

Witnesses saw the gunman run back to a Chrysler van and speed north through the alley. Surveillance cameras in the area captured a van matching the description of Willis’ girlfriend's vehicle fleeing the scene down 63rd Street, according to Kent.

Immediately after the shooting, Willis made phone calls to witnesses and arranged to have the van parked in an enclosed garage, where the license plates were removed from the vehicle, Kent said. Records show Willis' cell phone was pinging from towers in the area of the shooting at that time, Kent said.

Willis also made admissions to other people that he had seen Watkins driving in the neighborhood, went and got his gun and then opened fire on the van, Kent said.

Willis “told others that he would shoot the people responsible for the burglary of his mother’s Chatham home,” Kent said. “The defendant also told one of the people he believed was responsible for the burglary that he was ‘going to kill him’ when he caught him."

Law enforcement sources said whoever stole the game system sold it to someone else in the neighborhood. When the new owner hooked up the system at home, he saw it belonged to Willis, a fairly well-known figure in the neighborhood and a convicted felon with more than three dozen arrests dating to 1996.

Not wanting any trouble, the new owner returned the game console to Willis and told him the nickname of the person he bought it from, one of the sources said. Willis then figured out that person was Watkins, the source said.

Willis began questioning people about Watkins, and a short time later fired on Watkins' minivan as he sat with Jonylah in the front seat, police said.

Police have not located the van or the gun, Police Superintendent Garry McCarthy said Monday. Authorities identified Willis as a possible suspect early in the case, but they did not have enough evidence to charge him until detectives persuaded several witnesses to fully cooperate with the investigation last week.

Willis turned himself over to police Saturday, accompanied by his attorney. He did not give a statement, McCarthy said.

"Mr. Willis has been a suspect for a very long time," McCarthy said. "The question was whether or not we could show it in a court of law."

Investigators were able to track down acquaintances of Willis to aid in the case, a law enforcement source said. The acquaintances had earlier been stopped on the street by police while they had been with Willis and police had kept a record of those contacts. One of those acquaintances, who is on probation, told investigators last week that Willis spoke to him about how he shot Jonylah and her father, the source said.

Word had gotten back last week to Willis that investigators were putting pressure on his acquaintances, according to the source, before his lawyer agreed to turn Willis in to Area Central police headquarters on Saturday.

Willis, whose street nickname is “K.O Killer,” is a known Gangster disciple, according to court records. Prosecutors said his criminal record includes a 2002 conviction for aggravated assault of a police officer for which he received three years in prison. He also has several felony drug convictions, prosecutors said.

Willis’ attorney, Robert Fisher, told the judge he planned to argue for a bond at the next hearing, scheduled for June 6.

After court, Fisher said Willis voluntarily turned himself in to police on Saturday because it “was the appropriate thing to do” once he learned that detectives were looking for him. Willis made no statements to detectives before he was charged, Fisher said.

Fisher called the case “a horrible situation where a very young child was shot and killed,” but questioned why Willis was not charged until two months after the alleged crime.

“I suppose the only thing that could exacerbate the situation would be to prematurely charge somebody for that offense,” Fisher told reporters. “I’m sure the police were diligent from  the very beginning, and now all of a sudden either new witnesses…were discovered, or perhaps there are old witnesses that are making new stories.”

Like Hadiya Pendleton, a 15-year-old high school student fatally shot less than two months earlier, Jonylah made national headlines as yet another young victim of gun violence in Chicago.

More than 500 people were killed in the city last year, the vast majority by gunfire. It was the first time Chicago passed that number since 2008.