Sybrina Fulton, mother of Trayvon Martin, takes the stand during Zimmerman's trial on Friday, July 5. Zimmerman is charged with second-degree murder in the February 2012 shooting death of 17-year-old Martin. 
George Zimmerman's mother, Gladys Zimmerman, listens to the 911 tape while taking the stand during his trial in Seminole County circuit court on July 5. 
Martin's brother Jahvaris Fulton testifies at the Zimmerman trial in Seminole County circuit court on July 5. 
Volusia and Seminole County associate medical examiner Shiping Bao testifies on July 5. Bao conducted the final autopsy on Martin and determined the cause of death to be a gunshot wound to the chest. 
Florida Department of Law Enforcement Crime Lab Analyst Anthony Gorgone testifies about DNA findings on Wednesday, July 3, in Sanford, Florida. Here, Gorgone points to a sweatshirt worn by Trayvon Martin on the night Martin was shot. Only one stain on Martin's hooded jacket yielded a partial DNA profile that matched Zimmerman's. 
Gorgone points to a jacket worn by Zimmerman on the night of the shooting. Multiple stains on Zimmerman's jacket tested positive for Zimmerman's DNA. At least two stains from the jacket tested positive for a mixture of DNA that included Martin's DNA. 
Firearms analyst Amy Siewert from the Florida Department of Law Enforcement answers questions from the prosecution while holding Zimmerman's gun on July 3. Siewert examined the gun and said Zimmerman had one bullet ready to fire in the chamber as well as a fully loaded magazine when the shooting occurred. 
Alexis Carter, a military prosecutor, testifies during the trial on July 3. Carter taught a criminal litigation class that Zimmerman completed, and testified that the class included extensive coverage of Florida's self-defense laws. 
Mark Osterman, a U.S. Air Marshal and friend of Zimmerman's who wrote a book about the case, testifies on Tuesday, July 2. He recounted the story of the shooting that Zimmerman told him and testified that when he took Zimmerman home from the police station after the shooting, Zimmerman wasn't acting like himself. 
Prosecutor Bernie de la Rionda, on July 2, demonstrates a possible scenario while questioning state witness Chris Serino, a Sanford police officer. 
Hirotaka Nakasone, a voice recognition expert with the FBI, testifies in the Zimmerman trial on Monday, July 1. 
Witness Jonathan Good is cross-examined by defense attorney Mark O'Mara on Friday, June 28. 
Selma Mora reenacts a scenario for defense attorney Mark O'Mara on Thursday, June 27. Mora lived in Zimmerman's neighborhood at the time of the shooting. 
Witness Jennifer Lauer points to where her former home was in the Retreat at Twin Lakes community during questioning by defense attorney Mark O'Mara on June 27. Lauer called 911 on the night of the shooting. 
Rachel Jeantel, a friend of Martin's, is questioned by defense attorney Don West on June 27. She appeared to get frustrated several times during the cross-examination, including one time when West suggested they could break until the morning so she'd have more time to review the deposition transcript. 
The evidence letter that Jeantel says she wrote with a friend for Sybrina Fulton, Martin's mother, is displayed during the trial on June 27. When the defense asked Jeantel to read the letter, she said she couldn't read cursive. She asked a friend to write the letter for her, she said. 
Jeantel testifies on Wednesday, June 26. She was the last person to speak with Martin on the phone. 
Zimmerman walks past Martin's parents, Sybrina Fulton, left, and Tracy Martin, second from left, as he enters the courtroom after lunch recess on June 26. 
Diana Smith of the Sanford Police Department on Tuesday, June 25, shows the jury a bag of Skittles that was collected as evidence at the crime scene. Martin was said to be carrying the bag of candy and a soft drink at the time of his death. 
Assistant state attorneys John Guy, left, and Richard Mantei hold up Martin's sweatshirt as evidence during Zimmerman's trial on June 25. After Martin's death, protesters started wearing hoodies in solidarity against racial profiling. 
During the trial on June 25, crime scene technician Diana Smith shows the jury a gun that was collected as evidence. 
Zimmerman laughs with defense attorney Don West during his trial on June 25. 
Selene Bahadoor enters the courtroom to take the witness stand on June 25. She was the first eyewitness to testify and said the shooting occured right behind her home. 
Seminole County 911 dispatcher Sean Noffke testifies on Monday, June 24, about his conversation with Zimmerman on a non-emergency line the night of the shooting. 
A transcript of Zimmerman's police call on the night of the shooting is projected during opening arguments on June 24. 
Martin's father, Tracy Martin, cries on June 24 as he listens to the description of his son's death. 
Prosecutor John Guy gestures during his opening arguments on June 24. His first words to the six-woman jury may have raised a few eyebrows. "Good morning. 'F*****g punks, these a******s all get away,'" Guy quoted Zimmerman. "These were the words in this grown man's mouth as he followed this boy that he didn't know. Those were his words, not mine." 
From left, Zimmerman's father, Robert Zimmerman Sr.; his mother, Gladys; and his wife, Shellie, are escorted from the courtroom on June 24. Since they are all on the witness list, the judge ruled they cannot be present in the courtroom until after they testify. 
Defense attorney Don West displays a photo of Zimmerman from the night of the shooting during his opening arguments on June 24. He opened his statements with a knock-knock joke but failed to win a laugh. "Knock knock. Who's there? George Zimmerman. George Zimmerman who? Good, you're on the jury," he said. 
A video entered as evidence is displayed on June 24. It shows Martin, right, at a 7-Eleven on the night of his shooting. 
From left, Martin's parents, Tracy Martin and Sybrina Fulton, and Benjamin Crump, the family's legal counsel, make a brief statement to the media before jurors heard opening statements on June 24. 
Zimmerman waits for the start of his trial on June 24. 
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- Bob Greene: Zimmerman trial riveting, but why limit yourself to TV trials?
- He says in county and local courtrooms across U.S., trials constantly on display. Go watch!
- He says subjects are murder, robbery, financial shenanigans; it's free, tense, fascinating
- Greene: Beyond that, it's American justice carried out for us all; important to bear witness
Editor's note: CNN contributor Bob Greene is a best-selling author whose 25 books include "Late Edition: A Love Story"; "Duty: A Father, His Son, and the Man Who Won the War"; and "Once Upon a Town: The Miracle of the North Platte Canteen."
(CNN) -- It goes on every day, in every county in the United States.
It's absolutely free.
Usually there's no wait to get in.
And it can be as compelling as anything on television.
The Florida trial in which George Zimmerman stands accused of murdering Trayvon Martin is attracting large TV audiences. The O.J. Simpson trial got the country accustomed to watching high-profile court proceedings gavel-to-gavel; the trial of Jodi Arias drew big ratings before the Zimmerman trial.
Viewers return because they find the events almost hypnotic: something that thoroughly captures their attention.
But one of the so-omnipresent-that-we-seldom-think-about-it facts of American life is just how much human intrigue, how much tension, how much weakness and heroism and sadness and triumph are on continuous and ever-changing display in multiple and seemingly mundane settings all over the country, each day of the workweek.
And how relatively few people choose to sit in the first-come, first-served seats and take it all in.
The courtrooms of this nation, both criminal and civil, are bright stages upon which the theater of murder, deceit, heartbreak and duplicity are played out in excruciating and breathtaking detail.
If you're of a mind to, you can find on those stages narratives as spellbinding as any murder mystery in a bookstore or any crime drama in a movie theater. As a citizen, you can immerse yourself in the tale, day after day.
You have to have a little spare time on your hands -- maybe a few days away from work -- and you have to choose a case that most interests you from among the many that are going on at the same moment in the courthouse in your community. The clerk's office will have a calendar of the day's trials, and court employees can be helpful in explaining to you what is transpiring in the various rooms. Trials tend to have ebbs and flows, and there will be times when you have to be willing to sit through lulls.
But you will view and hear things more enthralling, more disturbing, more enlightening and more repellent than you might ever have imagined.
Moms take stand at Zimmerman trial 
State rests in Zimmerman trial 
O'Mara: I had to question Travyon's mom As a citizen in the seats, you will almost inevitably find yourself becoming a part of the cast of characters of the courtroom. A tangential part, to be sure. But after a few days the attorneys will begin to recognize you, as will the defendants, and the judge, and the bailiffs. You may begin to feel something close to a responsibility to show up -- a responsibility to yourself, not to miss a minute of the story you have started to follow.
Why don't more people, especially those who have the time, avail themselves of this opportunity?
Perhaps because they seldom stop to think it's there. When a big trial makes it to TV, the assumption is that it has some special quality to attract that spotlight.
That may be partially true. But although the sensational trials draw audiences because they're on television, there is so much to see and feel in the courtrooms of even the smallest cities and towns. The matters that bring people to trial -- whether acts of shattering violence, double-dealing in business transactions, any of the hundreds of variations of robbery and theft -- find their way to virtually every crossroads, and thus eventually into virtually every courthouse.
You can be captivated by just how skilled some attorneys are -- and surprised by just how ill-prepared some others are. You'll study the judge -- his or her shifting moods -- as if he or she is the protagonist in a paperback potboiler. You'll make eye contact with the defendants and the jury members.
And there is nothing quite like the moment when that jury returns with its verdict. This is a country that somehow becomes giddy when two singers face off in a televised talent contest, and one goes on to the next round while the other goes home. That feeling pales compared to the sensation of sitting in a courtroom, your vital signs kicking into a higher gear as the judge asks the foreman if there is a decision, and the seconds drag on before the words are read aloud.
The best part of the experience is that it's not taking place on a cold screen in front of millions of distant, unseen viewers -- it is unfolding a few feet from your eyes. Most cases, even in medium-sized towns, aren't covered by the local newspapers; there are just too many courtrooms for that.
But the curtain rises every morning, in public buildings everywhere in the U.S.
And, beyond the raw fascination of what goes on, there is another, much more vital, reason to attend:
Because someone should bear witness.
Because this is American justice, carried out in all of our names.
And anyone who cares to be there is always cordially invited.
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The opinions in this commentary are solely those of Bob Greene.
