Easily the most star-studded film playing within the confines of the Tribeca Film Festival, Lonely Hearts is based on the series of shocking murders perpetrated in 1948 and 1949 by Raymond Fernandez and Martha Beck. Before he met Martha, Raymond was making his living seducing women who wrote letters to “lonely hearts clubs” in search of love. After winning their trust, he would steal whatever he could get his hands on and disappear, moving on to his next victim. Though he met Martha via those same lonely hearts letters, the pair developed an intense connection and began to collaborate: Martha joined the scheme as Raymond’s spinster sister and, instead of just leaving their victims, they began to kill them. When the pair was finally caught in 1949, they proudly confessed to over a dozen murders.

The real Raymond was 34, sullen, unpredictable, and allegedly wielded complete control over his lover; in Lonely Hearts, he’s Jared Leto, who plays him as a lovesick puppy, less conniving than he is eager to please. Martha, meanwhile, was tragically overweight, so unattractive that in the early 1940s she was denied nursing jobs “because of her appearance,” and described in many accounts as Raymond’s worshipful “sex slave.“ In Lonely Hearts, by flawless Hollywood logic, she’s played by the stunning Salma Hayek, as an evil seductress who effortlessly compels Raymond to do her bidding. From first sight, then, it’s clear that director Todd Robinson is not interested in delving too deeply into historical events in his film. Instead, he tells two stories: one of them a titillating tale of murder and manipulation, and the other a quieter, more internal look at Elmer G. Robinson (John Travolta) and Charles Hildebradt (James Gandolfini), the fictional homicide detectives who solve the case.

As the film alternates between the two stories, it is the latter that is consistently the darkest both emotionally and visually, and eventually comes to dominate. The scenes away from Raymond and Martha are filmed with a dim pallet that enhances their hopelessness and effectively gives them a period feel. Deeply troubled by the suicide of his wife three years earlier, Robinson has been going through the motions for months; the Lonely Hearts case marks his first venture into the field since her death. His depression dominates these segments of the film, and is well-played by a pallid, lumpy Travolta. As his partner, Gandolfini is wonderful, turning in the sort of nuanced, affecting performance that we’ve come to expect from him, offering support but still questioning the roots of Robinson’s sudden obsession with this new case.

When the camera turns to Martha and Raymond, things are different. Visually, their scenes pop with color (often the red of splattered blood is prominently featured), and are vivid with emotion. Hayek: is magnificent, gorgeous, seductive, and utterly without shame. She plays her role to the hilt, clearly thrilling in the power it allows her to wield. Had director Todd Robinson chosen to focus the film on her, it could have been a very different, wonderfully audacious project.

Though he is its early star, Jared Leto is unfortunately the film’s weakest link, and struggles not to vanish completely next to Hayek’s explosive, deliciously self-assured performance. He gamely undertakes the part of Raymond, hiding his good looks behind a receding hairline and seedy mustache, but is unable to embraces the character’s complex combination of weakness and power. Instead, he favors volume and physical explosions over any suggestion of subtlety, a tendency that dramatically reduces the power of what is, on paper, a disturbing story.

Despite its three good central performances (not to mention strong supporting turns from Scott Caan as a young, obnoxious cop, and Laura Dern as Travolta’s love interest), the film generally fails to engage, and feels much longer than its 100 minutes. Both storylines, initially, are interesting, with Martha and Raymond in the early throws of their romance, and the detectives bantering in the stereotypical (but nevertheless appealing) style favored by New York cops, at least in the movies. Before long, though, both slow to a crawl, highlighted only by periodic bloody explosions that seem totally arbitrary in their graphicness -- it feels as if the film’s makers recognized its slow pace, and mistakenly believed the blood would be enough to keep our attention.

In the end, the decision to focus on Raymond, and then on the emotional struggles of Travolta’s character costs Lonely Hearts, depriving it of the tantalizing, cheeky glee of some early scenes, particularly those featuring Hayek at her most audacious. What could have been a thrilling exploration of remorseless female power is instead rendered a rather pedestrian, if well-acted, story about a midlife crisis, acted out against a backdrop of unexamined serial-murder.