Law in action, legal perspective

According to the “law in action” legal perspective, criminal procedure is a dynamic process often referred to as the “criminal justice funnel,” in which almost all cases enter the criminal justice system at the top of the funnel, but many are eliminated along the way during their move through the legal system (a process called “case attrition”) with only a few actually making it to trial, and even less seeing conviction that results in prison sentencing. List three primary reasons for case attrition, explain how they operate, and state whether or not you believe this is a pro or con to our legal system?