why did stacey seem upset while he and his family were visiting the ellises and mrs.lee annie?

The children start talking about TJ Avery and how he is in prison. TJ claims RW and Melvin Simms killed Mr. Barnett and robbed the store in Strawberry but nobody would believe a poor black boy's word over a white boy's word. Thinking about this angers Stacey. The injustice of it all makes him mad.