Why is Lace jailed in the novel, The Vig?

Lace is a kid who lives in the projects and works for Dido. Lace is convinced that Louis Baker killed Dido until a new drug dealer approaches him about staying quiet about the murder. Lace thinks that this new drug dealer, Samson, killed Dido and he goes in search of Samson's gun. When Lace finds it, he takes it to Mama who is the woman that Baker lives with. However, she tells Lace that there is nothing anyone can do. Lace takes the gun and shoots Samson with it, clearing Baker's name, but getting sent to jail himself.