Paul Lieberman is a feature writer who spent 24 years covering a variety of beats at the Los Angeles Times. He has won a fistful of awards plus a Nieman Fellowship and was on two reporting teams that were awarded the Pulitzer Prize.

Back in 1992 the paper had just run a story about how the Intelligence unit of the Los Angeles Police Department was digging up dirt on various celebrities and politicians around town while monitoring organized crime. The piece said the practice started back in the 1950s. A few days later, Lieberman received a call from a dissenting reader. “A quavering old man’s voice on the other end said to me, ‘You’ve got it wrong. That goes back to right after World War II and the Gangster Squad.’ ‘How do you know?’ I asked him. ‘Because I was there.’”

So began a 15-year reportorial odyssey in which Lieberman reconstructed the saga of the LAPD’s “Gangster Squad,” which started as an eight-man unit in 1946 and eventually expanded to more than 50 members before being folded into the tamer Intelligence Division after the U.S. Supreme Court placed restrictions on searches and seizures. The Squad’s mission was to investigate, harass, and otherwise make life difficult for the mobsters who were starting to filter into Los Angeles from other parts of the country. Chief among them was Mickey Cohen, a 5-foot-5-inch former flyweight boxer who wore a Star of David on his trunks and was threatening to bring Chicago-style crime to the West Coast’s “Garden of Eden.”

Gangster Squad, which just opened with Sean Penn as Mickey, is supposedly based on Lieberman’s fifteen-year labor. “Inspired by a True Story” is what it says in the opening titles, but at the end of the final crawl there’s another notice saying, “The characters depicted in this film are fictional and any resemblance to any real persons… etc.” The latter comes much closer to the truth.

The fellow on the other end of the line that day was John O’Mara, a World War II code-breaker who had reclaimed his job with the LAPD in 1946. One day O’Mara and 18 other officers were called into a room and told they were candidates for an elite squad that would pursue and harass gangsters, working pretty much on their own, in secret and without badges. After some sorting out, eight took the assignment. “They were given two old unmarked police cars with rusted-out floorboards,” says Lieberman, whose seven-part series finally ran in 2008, followed by a book, Gangster Squad, just published by St. Martin’s Press. “Whenever they drove through a puddle, they had to hold their feet up to avoid getting splashed.”

O’Mara was one of two quarterbacks. The other was Willie Burns, a gunnery officer from World War I who had participated in the “Bum Blockade,” when Los Angeles tried to prevent hoboes from migrating to California during the Depression. Jerry Thomas had a photographic memory and could come out of a bar after a two-hour undercover operation and recite the entire conversation. Con Keeler was an electronics genius who could manufacture bugs out of hearing-aid parts and telephone diaphragms and relay the signal to a garage listening post. “For ten years he refused to talk to me,” says Lieberman. “Then one day he opened up and never stopped after that.”

Finally, there was Jumbo Kennard who, the son of a Texas constable, had worked as a roughneck in the Oklahoma oil fields. At six-foot-four, he could pick people up by placing his giant hands over their heads. “It was basically a few smart guys plus a lot of muscle,” says Lieberman. Later came Sgt. Jerry Wooters, a roguish vice cop and ladies’ man, portrayed in the movie by Ryan Gosling. Seeing the war coming, Wooters had signed up to shoot instructional films for a reserve unit at a movie studio, confident he would spend the war on a Hollywood lot. But he made the mistake of arresting a judge’s nephew and, in the manner of that era, was immediately reassigned to taking reconnaissance photos out the door of a bomber over the Pacific. Twice he was shot down but rescued by American ships before meeting the Japanese and certain death.

If they were a colorful crew, so was their main adversary, Cohen. A poor boy from Brooklyn, he had started fighting at age 6 to defend his newsboy’s turf. At 19 he made his way across the country, fighting professionally, until finally meeting the Capone crowd in Chicago. They signed him on as a foot soldier but his big break came when Meyer Lansky sent him to L.A. to help Bugsy Siegel set up gambling operations. But Lansky soon became suspicious that Siegel was squandering his money on the lavish Flamingo Hotel in Las Vegas and had Siegel rubbed out. One story has it that Cohen was so enraged he charged into the Roosevelt Hotel where he thought the assassins were hiding and fired a few shots into the ceiling, demanding their appearance. Nobody responded and when the cops arrived a few minutes later he fled. That was his most flagrant act of public violence.

Not that Cohen shrunk from confrontation. When fellow bookie Maxie Shaman stormed into the paint store that fronted for a horse betting operation, Cohen put a bullet in him. He told the cops it was self-defense and was never prosecuted. In Los Angeles and other cities of that era, the rule was, “It’s alright as long as they only kill each other.” The gangsters could shoot it out among themselves but if the bodies started turning up on the street, the law cracked down.

Through the late 1940s and 1950s, the Gangster Squad harassed and intimidated various hoods, trying to keep things at a minimum. One favorite tactic was to take a newcomer from Chicago or Rhode Island into the hills overlooking LA, put him on his knees and stick a gun in his ear. “Do you feel a sneeze coming on?” O’Mara would ask his charge. “A… real… loud… sneeze.” Then he would tell him to get out of town. “It was the most colorful piece of genuine dialogue that survived into the final script,” says Lieberman. But Josh Brolin, playing O’Mara, didn’t like the line and so it was dropped. So much for being inspired by true stories.

By the mid-1950s, Cohen was aspiring to a respectable notoriety. He allowed Life magazine to do a feature on his home and pet dogs and Mike Wallace had Cohen as one of the first guests on his new TV show. But the squad had laid a trap. O’Mara had gotten one of Mickey’s guards to sneak seven guns out of the house on the pretense that they needed cleaning and test firing. Then he etched initials underneath the butt plates so they could be tied to Mickey. Almost ten years later, two of those guns turned up when Jack “Enforcer” Whalen was gunned down in a public restaurant. Everyone at the table exonerated Mickey and one of his henchman confessed to the shooting, but the etched guns were found nearby and Cohen was tried for conspiracy. Sitting in a barber’s chair awaiting the sequestered jury’s verdict, he famously remarked, “What a great country. They lock up the jury and let me go free.” The jury hung.

Over the years, the Squad became so familiar with the mobsters that they liked to play pranks on them. “One of their favorites was to find an Illinois license plate, stick it on an old unmarked car and have a pair of Squad members drive into the neighborhood of Cohen’s storefront,” says Lieberman. “They would park a block away with their hats pulled down over their faces and wait for Cohen’s foot soldiers to start checking them out. Then they would pull out and roar past the store, waving their Tommy guns. It was just to mess with Cohen’s head.”

The spying and harassing continued until the 1950s, when one of Wooters’ warrantless buggings was challenged in the California Supreme Court. Anticipating the U.S. Supreme Court’s 1961 Mapp vs. Ohio, the California judges threw out the evidence as illegally tainted. It was the beginning of the end. “They knew their days were over,” says Lieberman. “O’Mara said that dogging criminals wasn’t fun anymore.”

An interesting piece of American noir from another era, right? Now let’s see what happens in the movie,

On the big screen, the tight-knit group that roughed up suspects and conducted illegal searches has been transformed into another gang that rampages across Los Angeles busting into gambling parlors with Tommy guns and shooting indiscriminately at patrons. In one scene they burst from behind the stage at a nightclub where a Carmen Miranda look-alike is singing a Latin number. Another scene had the bad guys luring the cops into Grauman’s Chinese Theatre, where they fired at them through the movie screen. That scene got yanked after James Eagan Holmes did almost the same thing in Aurora six weeks before the film’s first scheduled opening in September. The premier was postponed until last week.

Meanwhile, Cohen, who undoubtedly killed at least one fellow hood but liked to claim more, has been turned into a contemporary Vlad the Impaler. In the opening scene he has a Chicago gangster torn in half by two opposing cars the way people used to be quartered by horses during the Middle Ages. Director Ruben Fleischer collected a teenager audience with Zombieland and apparently didn’t want lose them to The Texas Chainsaw Massacre. During the remainder of the film, Penn: 1) incinerates a clumsy lackey in an elevator shaft, 2) orders his boys to put an electric drill through the head of a rival gangster (“You know the drill,” he tells them), and 3) mows down street crowds, including an innocent newsboy whose death finally persuades Gosling/Sgt. Wooters to join the squad. All this is carried out amid the predictable car chases, fiery smash-ups, and the explosion of a truck carrying a (fictional) heroin shipment that levels half a block of Chinatown. (Cohen was not known to deal in drugs.) Instead of just a crime boss trying to muscle other mobsters out of the bookmaking and extortion rackets, Cohen becomes a Batman-style overlord trying to bring the whole city to its knees.

In the final scene — perhaps inspired by Cohen’s putting two bullets in the ceiling of the Roosevelt — the Gangster Squad launches a full-scale attack on Cohen’s hideout in the historic Park Plaza Hotel. Blessedly, the hotel staff and guests have gone home for the weekend, leaving the rival gangs to shoot it out. Their Tommy guns bring down chandeliers and shred the Christmas decorations, killing at least a dozen, until — inevitably — O’Mara and Cohen finally duke it out with fists. All this to serve Cohen with an arrest warrant.

I came out of the movie theater with the same feeling I used to get reading the old horror comics of the 1950s. Until the industry voluntarily regulated itself in 1954 with the Comics Code Authority, it had turned out “comics” where bug-eyed victims would have their flesh picked clean by piranhas or their heads bashed in with baseballs. My elderly piano teacher had a stash in his parlor and every week while my sister was taking her lesson I would be hypnotically drawn into the pile where I pored over sickening scenes of blood and mayhem until I was nauseous. I always left saying, “I wish I hadn’t done that.”

So where in the annals of American history has there ever been a scene where rogue cops and gangsters shot it out for twenty minutes in the lobby of a major hotel without the regular police even bothering to show up? The answer is simple: 1) in the movies, and 2) in the minds of teenage boys, the sickest of whom will one day decide to act out such a scene himself. O’Mara’s granddaughter has written a long protest on Reddit complaining of the misrepresentations, but who cares? Hollywood does what Hollywood does. Asked if the industry could have made a more realistic film out of his 15 years of research, Lieberman says, “If a studio spends $75 million, they’ve got the right to make the film they want.”

“Think Global, Kill Local” was the poster for one movie showing the day Adam Lanza shot up Sandy Beach Elementary. In Hollywood, even Hansel and Gretel are now vengeful superheroes. Recently about 25 movie stars made a TV commercial in which they appeared in quick succession pleading for gun control to “end the violence” and “protect the children.” On the Internet, some clever wag has interspersed the ad with movie scenes in which the same actors and actresses spout their love of guns and plaster the landscape with bullets. It’s good entertainment. It also suggests that if you want to stop the next lunatic from killing a dozen or more innocents, the best place to start might be in that moral sewer on the west side of Los Angeles.