It has taken four decades for Robert De Niro (2007's "Stardust") and Al Pacino (2008's "88 Minutes") to find a feature film vehicle for them to headline together (their brief scene in 1995's "Heat" doesn't count). If "Righteous Kill" was the best one offered to them, then it's safe to say they're ready for retirement. This is an astonishingly inept and ill-considered motion picture, a thriller that fails to thrill but successfully confounds viewers at the level of amateurishness up there on the screen. Writing, direction, acting, editing—there is scarcely a nice thing to say about any of it. Laughter is the only option outside of prematurely fleeing the theater.

On the streets of New York, a serial killer is popping bullets into the city's morally corrupt citizens. Veteran detectives Turk (Robert De Niro) and Rooster (Al Pacino)—yes, those are the names they go by—are assigned to the case. Right from the start, in grainy footage made to look like a confession, Turk admits to the crimes and gradually explains the sordid path taken to becoming something of a vigilante on the side. Because it will be exceedingly obvious for any viewer who has ever sat down and watched a movie, it shouldn't be giving anything away to say that this is merely a plot device. Do you really think director Jon Avnet (who previously guided Pacino down a path of mediocrity with the aforementioned "88 Minutes") would reveal whodunit from the very beginning? Of course not. What's more, the actual culprit is so obvious from frame one that when it is treated as some kind of shocking twist in the third act, all one can do is smack their forehead and ruefully shake their head.

One of the most patently imbecilic thrillers to come down the pike in many a moon, "Righteous Kill" is stunningly boring at the onset before it sinks to the depths of unintentional camp. Looking haggard, exhausted and unfailingly disinterested, Robert De Niro and Al Pacino have become parodies of their powerhouse former selves. They are terrible as partners Turk and Rooster—their ending scenes together might be as shockingly bad as they've ever been on film—though, to be fair, they don't exactly have Oscar-caliber material to work with. Strictly two-dimensional, their characters listlessly mug and stumble their way through a tired narrative that goes nowhere, offers nothing of interest, and introduces nada to think about. Perhaps De Niro's only reason for choosing this role was the simulated sex scenes he gets to perform with the gorgeous, barely-half-his-age Carla Gugino (2007's "American Gangster"). Pacino doesn't even receive the pleasure of that much. Any way you swing it, it's clear the once-mighty have fallen on hard times.

The pitfalls don't end with the two leads. Claustrophobically shot primarily in interior locations or on nondescript streets, the film's look is shoddy and dull. Though set in New York City, it could have just as easily been shot in Cincinnati and no one would be able to tell the difference. Meanwhile, Jon Avnet directs as if he has come unprepared and with no idea what he's doing. Editing is just as clunky, cutting from one scene to the next with no fluidity and only minor consideration for what has come before and is about to follow. The screenplay by Russell Gewirtz (2006's "Inside Man") is riddled with plot holes, contrived developments, and without even passing consideration for logic.

Dialogue is so bad as to not be believed, and the weak acting all around doesn't help matters. In one sequence, Rooster taps on the metal bar of an opened jail cell, making Karen Corelli (Carla Gugino) jump. "That's the first time I've ever rattled someone's cage," he says. In another moment, Turk hands money to a grieving mother (Melissa Leo) who has recently lost her child and tells her to go drink herself to death. This is treated seriously, or at least it seems to be. You simply can't make this stuff up. As Spider, a high-price drug dealer and club owner, recording artist Curtis "50 Cent" Jackson (2005's "Get Rich or Die Tryin'") proves that he has no place in front of a movie camera. His embarrassing performance is so wooden that he might as well be playing Pinocchio. Also set adrift into the proceedings, John Leguizamo (2008's "The Happening") and Donnie Wahlberg (2007's "Saw IV") look lost as detectives Perez and Riley, there to basically aim a suspicious eye at Turk when it is discovered that the killer might be working on the police force.

"Righteous Kill" only gets worse as it crawls to the finish line. In a hoary cliché made hoarier by the over-the-top script, the newly unveiled killer drones on and on describing the motives that have led him to take fourteen lives. This is followed up with a hilarious chase scene in which actors past middle-age briskly walk rather than run in lukewarm pursuit, one of them unfortunate enough to be wearing a ridiculous sweatsuit. If it weren't so silly it would actually be depressing to behold. "Righteous Kill" is what happens when a heinously misguided project is greenlit before saner minds have prevailed.