2 questions
What was in the hole wrapped in plastic?
Why did he kidnap Sanaa Latham's character? She had nothing to do with the incident.
Angel Sanchez's (Forest Whitaker's) mother was in the hole, wrapped in plastic. My guess is that this was to even further prove Angel isn't right in the head. Of course, this is left to interpretation, just as who exactly it was that was shot at the end of the movie. The movie just sucked at making people even want to interpret any of the unanswered questions.
He kidnapped Sanaa Latham's character (and Mike Epps' character) to bring the family all together, just as Anthony Mackie's character had done with Angel and all of his family earlier in the movie.