The story you've just seen is true. The names were changed to protect the innocent.
In the late 1960s and early 1970s a man named Jack Webb produced two television series. Both shows were based on the files of the Los Angeles Police Department. Both incorporated the quote above. One of the series, known as Adam-12 followed police officers Reid and Mulloy on their daily patrols of Los Angeles in their squad car numbered 1 A-12, AKA 1 Adam-12. The other, staring Webb himself as Sgt Joe Friday and Harry Morgan - who later played Colonel Sherman T Potter on M*A*S*H) - Bill Gannon, as his partner, was a detective drama known as Dragnet.
Just the Facts...
Dragnet's episodes used detectives Friday and Gannon as vehicles to show off the heroics of the detectives of the LAPD. The crimes they solved really occurred, the criminals they arrested were really apprehended, and in nearly every case convicted in a court of law. Each episode followed essentially the same formula around the basic structure of the official report.
This is the City...
Each episode of Dragnet opened with a monologue by Jack Webb as Joe Friday. 'This is the city: Los Angeles, California. I work here. I carry a badge.' Some episodes got a long monologue, others got the one just mentioned. All monologues began and ended with the same lines. In the longer bits, Friday would wax poetic about LA - either its many job opportunities, its suburbs, or its many diverse cultures. Inevitably he'd light upon something - usually having to do with hippies. Joe Friday hated hippies - that would remind him of crime. 'That's when I go to work. I carry a badge.'
After the monologue, the opening credits would roll over a picture of Joe Friday's badge1. Afterwards, Friday would fill us in on the situation at hand. The format of the show required that he and his partner, Gannon, be switched around between departments depending on where the case that the show's writers had found this week had been investigated. Sometimes they were working out of homicide, other times Fraud, or Missing Persons. The set-up portion of the show brought us up to speed on where and when they were working. He'd also set up Bill's bit for the episode.
Bill Gannon's Bits
Officer Bill Gannon was, with the exception of the occasional eccentric witness, the show's closest thing to 'comic relief'. Officer Gannon, though outranked by Friday and who was a bit older and the only one of the two who was married, would generally begin the episode with something that Joe found amusing. Bill dabbled in isometrics and other modern remedies to common problems. He also had some of the worst eating habits known to the LAPD.
...and the Show Begins
After Bill and Joe get done chatting, a call comes in2 and the show gets rolling. To keep the serious television viewer involved in the show's reality, Sgt Friday would regularly inform the audience of the time of day at which each event depicted occurred. This is all well and good if you're watching for reality. But watching a re-run of Dragnet is usually more fun from the 'tongue in cheek' perspective. In this case, you'll want to keep score of some of the more clichéd scenes, such as...
The Nod - The most common Dragnet fallback gesture. 'The Nod', true to its name, is a nodding of the head, coupled with a thoughtful expression on the face - usually Bill Gannon's - occurring after Sgt Friday had made a very insightful comment. However, 'The Nod' can also be a head shake which the detectives display to show their disapproval at a criminal's lame explanation of their motives.
The Eccentric Witness - Usually an elderly woman who has absolutely no idea what's going on. Sometimes she wants nothing more than to help the police apprehend the bad guys. Other times she will have nothing to do with the cops. She's been a religious zealot, and a widow with a tremendous fortune, a woman with no hearing, and a woman with total disregard for her own money.
'Just the facts, Ma'm' - A rarer scene than you might think
A Strong Anti-Drug Message - This one goes with the anti-hippie message of the entire show. Joe Friday really rants on sometimes. 'Marijuana is the flame! Heroine is the fuse! LSD is the bomb!'
Joe's Walk - Like the Grinch's heart, this man's underwear is two sizes too small.
The Detectives at Home - This is when you need to find something else to watch. If the characters aren't on duty, and are, instead, spending the evening in each other's company, there's no show. Sometimes what you get is a series of small disturbances that the neighbours ask our heroes to investigate. At least once there was an entire episode where the only crime committed was a misdemeanor, and the first 20 minutes of the show was pure fluff.
The Wrap Up
So Joe and Bill have got their man. Once again they've saved the day. The voice-over guy informs us that the story we have just seen is true, and tells us that 'on date 'x' a trial was held in court 'y' in and for the county of Los Angeles. In a moment, the results of that trial.' Then you get a nice commercial break, after which the voice-over guy tells you who was convicted of what, and what sentence they received. Roll credits, play that theme music.
There was a movie made of Dragnet, starring Dan Akroyd as Joe Friday the nephew of the original, late, Joe Friday. Tom Hanks plays his oddball, 'shoot from the hip partner', Striebek, and Harry Morgan makes an appearance as Captain Bill Gannon. It's a comedy, of course, and though the story you get to see isn't quite true, it's a great laugh.