A hardcore gangster film could hardly be expected to open with schoolchildren frolicking on a playground. Appropriately, “American Gangster” hits the audience with a scene in which an unidentified, severely beaten man is doused in gasoline and then lit on fire.

The latest from director Ridley Scott (“Black Hawk Down” and “Gladiator”) is awash in cold-blooded violence and graphic drug abuse. Brilliantly ambiguous, “American Gangster” at once dives into the mysterious world of drug lords and urges the audience to question preconceptions about morality.

The true story of 1970s drug lord Frank Lucas (Denzel Washington) and police investigator Richie Roberts (Russell Crowe) spans several years, seamlessly jumping from the boroughs of New York to Bangkok and back again in a matter of seconds.

Lucas monopolizes the heroin market by going directly to the source: Vietnam. His brand of dope, “Blue Magic,” hits the streets, and Lucas prides himself on selling heroin twice as good for half the price.

Roberts, a detective above the petty bribes and crooked dealings of New York’s police force, finds himself involved in a federal drug trade investigation. His thorough and incisive observations of the heroin scene eventually lead him to suspect kingpin Frank Lucas, and his efforts to bring him down ensue.

Dropping his Aussie accent (and his phone-throwing temper), Russell Crowe transforms himself into a down-on-luck special investigator. From his casual shoulder shrugs to the bad-ass way he saunters down the street, Crowe’s mannerisms reveal a man morally superior to the average cop. Washington’s performance similarly succeeds at pinning down his character’s superhuman fearlessness. Except for when he’s taking his mother to church or playing ball with his nephew, Lucas barely cracks a smile, refusing to allow his business persona any glint of emotion. Even while abruptly murdering a bankrupt debtor in broad daylight, Lucas does not flinch.

The film’s abrupt transitions highlight the murky moral issues at stake, but unfortunately sacrifice continuity. A heroin user injecting a needle into his foot and laying back in drug-induced ecstasy interrupts a scene of Lucas’ family eating dinner. In moments like this, Scott juxtaposes the graphic, yet distant and impersonal, world of addiction with the film’s quiet, domestic moments. If Scott attempts to shock the audience, he succeeds. Although these abrupt scene changes quicken the pace of the film, they break the flow of the plot. At the same time, though, these graphic images remind us that Lucas’ decisions and actions have a decisive impact on other people.

Scott cleverly uses cinematic techniques to contextualize the film historically, but sometimes his efforts come across a little forced. Strategically placing characters next to radios and televisions broadcasting nationwide drug problems associated with the Vietnam conflict, Scott repeatedly points to a broader conflict at work in “Gangster.” Heroin in American drug culture, the film repeatedly suggests, is directly related to soldiers’ abuse of the drug while serving in Vietnam. At times skillfully employed, these juxtapositions, when overdone, seem like a weak attempt to convey a historical message.

Itself something like a shot of heroin, “American Gangster” leaves us wanting more — more of Denzel and Russell, more of the story, more of the drama. More importantly (and less euphorically), “Gangster” leaves us questioning our moral sympathies.