In the 1981 police drama, “Prince of the City,” both cops and criminals use plenty of four-letter words.

But the word both groups consider the most obscene is spelled is spelled with three letters: R-a-t.

The movie is based on the true-life story of former NYPD detective Robert Leuci (“Danny Ciello” in the film, and played by Treat Williams).  It’s based on the best-selling nonfiction book, Prince of the City, by Robert Daley, a former deputy commissioner with NYPD.

Leuci/Ciello volunteers to work undercover against massive corruption among lawyers, bail bondsmen and even his fellow narcotics agents.

Along the way, the movie gives viewers numerous insights into not only how real-world cops work but how they see the world–and their role in it.

Robert Leuci (“Danny Ciello” in “Prince of the City”)

In its first scenes, “Prince” shows members of the elite Special Investigating Unit (SIU) preparing for a major raid on an apartment of Columbian drug-dealers.

Ciello, sitting in a restaurant, gets a tip on the Columbians from one of his informants.  He then phones it in to his fellow officers.  Together, they raid the apartment, assault the dealers, and confiscate their drugs and money.

The film makes it clear that even an elite detective squad can’t operate effectively without informants.  And in narcotics cases, these are either addicts willing to sell out their suppliers or other drug-dealers willing to sell out their competitors.

For the cops, the payoff is information that leads to arrests.  In the case of the SIU, that means big, headline-grabbing arrests.

Drug raid

With their superiors happy, the stree-level detectives are largely unsupervised–which is how they like it.  Because most of them are doing a brisk business shaking down drug-dealers for their cash.

For their informants, the payoffs come in several forms, including:

• Allowing addicts to continue using illegal drugs.
• Supplying addicts with drugs, such as heroin.
• Allowing drug-dealers to continue doing business.
• Supplying drug-dealers with information about upcoming police raids on their locations.

All of these activities are strictly against the law.  But to the men charged with enforcing anti-narcotics laws, this is the price to be paid for effective policing.

But not all police informants are criminals.  Many of them work in highly technical industries–such as  phone companies.

A “connection” such as this is truly prized.  With it, a detective can illegally eavesdrop on the conversations of those he’s targeting.

He doesn’t have to go through the hassles of getting a court-approved wiretap.  Assuming he has enough evidence to convince a judge to grant such a wiretap.

A top priority for any cop–especially a narcotics cop–is protecting the identities of his informants.

At the very least, exposing such identities could lead to embarrassment, unemployment, arrest and imprisonment.  At worst, it could lead to the murder of those informants by enraged criminals.

But there is another reason for protecting the identity of informants: The cop who amasses a roster of prized informants is seen as someone special within the police department, by colleagues and superiors alike.

He knows “something” they do not.  And that “something” allows him to make a lot of arrests–which, in turn, reflects well on the police department.

If those arrests end in convictions, his status within the department is further enhanced.

But while a cop is always on the lookout for informants against potential targets, that doesn’t prevent him from generally holding such people in contempt.

“Rats,” “finks,” “stool pigeons,” “canaries,” “informers”–these are among the more printable terms (for most media) cops use to describe those who betray the trust of others.

Such terms are never used by cops when speaking to their informants.

For cops, the most feared- and -hated part of every police department is its Internal Affairs Division (IAD).  This is the unit charged with investigating allegations of illegal behavior by police.

For most cops, IAD represents the devil incarnate.  Any officer who would be willing to “lock up” a “brother officer” is considered a traitor to the police brotherhood.

Even if that “brother officer” is engaging in behavior that completely violates his sworn oath “to protect and serve.”

In “Prince of the City,” Danny Ciello gives voice to just these feelings.

He’s preparing to betray the trust of his fellow narcotics officers by exposing the massive corruption among them.  Yet he fiercely rejects the idea that he is a “rat.”

“A rat is when they catch you and make you an informer,” he tells his wife.  “This is my game.”

Ciello has volunteered to obtain evidence of corruption; he’s not under some prosecutor’s thumb.  That, to him, makes him different from a “rat.”

Of course, once Ciello’s cover is blown and his fellow cops learn what he has done, they will forever brand him a “rat,” the worst sort of turncoat.

The movie ends with Ciello now teaching surveillance classes at the NYPD Academy.  A student asks: “Are you the Detective Ciello?”

“I’m Detective Ciello.”

“I don’t think I have anything to learn from you.”

For viewers seeking to learn the workings–and mindsets–of real-world police agencies,  “Prince of the City” has a great many lessons to teach.