Who killed the drugstore owner in the novel Monster by Walter Dean Myers?

Walter Dean Myers' Monster tells the story of the murder of Aguinaldo Nesbitt, the proprietor of a drug store. Steve Harmon and Osvaldo Cruz are on trial as accessories to the murder, which was committed during the commission of a robbery. James King and Richard "Bobo" Evans were both involved in the theft.
During the trial, Bobo testifies that King took Nesbitt's gun and shot him. According to Bobo, King was high on "crank" and believed that Nesbitt was a physical threat. Bobo implies that this interpretation was likely due to the fact that King was on drugs at the time and perceived a risk that did not exist.
Myers never explicitly states who pulled the trigger. The detectives involved in the case were unable to retrieve any hard evidence, relying stead on eyewitness testimony. The jury finds King guilty, and he's sentenced to 25 years to life in prison.

In the novel Monster, Richard "Bobo" Evans testifies that James King shot and killed Aguinaldo Nesbitt. Bobo tells Petrocelli that King smoked some "crank" before they entered the store. Upon entering the store, King began arguing with the store owner while Bobo reached for the money in the cash register. Bobo says that he heard a shot and turned around to see King holding a gun. After the robbery, Bobo said that he asked King what happened, and King told him that the store owner tried to "muscle him." When Asa Briggs cross-examines Bobo, Bobo tells Briggs that the reason King shot the store owner was because he was high.
The detectives were not able to retrieve any fingerprints from the scene of the crime and the gun legally belonged to Nesbitt. Myers does not clearly state that James King pulled the trigger, which makes the question of who killed Nesbitt ambiguous. However, the jury ends up finding James King guilty of felony murder and sentences him to 25 years to life in prison.