Dressler, p. 6-8, “Criminal Law in a Procedural Context: Pre-Trial”
Only a small minority of crimes ever result in a trial. Even if a crime is reported, the quality of the investigation of the crime can vary based on many factors, including some that are unfair.
Not every investigation results in enough evidence to make an arrest. You can’t arrest a suspect without probable cause, which basically means that there is a strong chance the suspect actually did the crime you’re investigating.
Not every arrest results in a trial. The suspect may get a preliminary hearing where the judge decides whether or not the arrest was justified. Then in most jurisdictions the trial goes to a grand jury. The grand jury must indict the suspect in order for them to be brought to trial.
Not every indictment even results in a trial. The suspect can file some pretrial motions, and some of them have the potential of getting the charges thrown out.
At that point, a lot of defendants plead guilty, so there is no trial. The prosecutor and defense attorney may make a plea bargain. Generally speaking, the conviction rate from guilty pleas is around 90%.
 Does this mean that 90% of all convictions come from guilty pleas, or does this mean that 90% of those who plead guilty are convicted? I think the former, but it’s not clear from the text.