If you're a cop at a crime scene, don't use black or silver tape — use red. For reasons known only to them, killers love black and silver tape for binding victims' hands, feet and mouths; you don't want to get your tape mixed up with theirs.

Director Ami Canaan Mann learned this dark detail and more at “homicide school,” the series of classes that beginning detectives take to learn the gory tools of their craft — murders and the investigation thereof. Mann was there doing research for her new film, Texas Killing Fields, about two detectives (played by Sam Worthington and Jeffrey Dean Morgan) tracking a killer who dumps his victims' bodies in a marsh. The film is not only inspired by true events but informed by them.

Riding along with the police one night, she got lucky — if “lucky” is what you call a double homicide in Commerce. Two bodies in an SUV. The corpses had been rotting for several days. “It was great,” she says.

Sitting on the sidelines, she learned how slowly everyone moves. They took their time, scrutinizing everything. “There's no bravado walking onto the crime scene. No coming to rapid conclusions.” Just the slow, methodical spreading of an intellectual net around the evidence. That thoughtfulness surprised her and found its way into the film.

Also surprising: how dapper the sheriffs and detectives dressed. Not in Armani like the guys on TV, but nice. She asked them about it. They told her, if they're going to have to knock on a stranger's door and inform them their son is dead, they're going to do it with respect.

When you're building a world, details matter. But which ones? The filmmaker watched how long people spoke to each other — the CSI techs, the detectives, the cops, the coroners, the myriad players in the theater of tragedy. She noted how shiny their shoes are. What kinds of notebooks and pens they use. What items they have hanging on their cars' rearview mirrors. If they wear a hat. How loudly they speak and to whom, if anyone, they raise their voice. The officers and detectives, she remembers, spoke in hushed tones. No yelling. In deference to the dead, who can't even hear.

Sometimes details are just plain details — a devil to sort out. Other times, they have God in them, and ought not be overlooked. The guns, for instance. What kind of gun would her lead character, Detective Brian Heigh, use? The characters in Mann's film are modeled on real people, and the real-life detective Heigh uses his father's old Colt revolver. Why carry this old-fashioned firearm into battle when the bad guys are loaded up with the latest automatic this and that?

“Because he doesn't ever want to have to fire it,” Mann says with satisfaction. Though its provenance is never explained, and you only see it for a few seconds, the revolver (or a prop replica of it) made its way into her movie, too.

Not everything gets screen time. Poking around at the county morgue, Mann noticed a severed limb in a plastic bag. It firmed up her conviction that no one actually needs to see a severed limb. “I'll never get that out of my head,” she says now, leaning forward onto the table, all elbows and intensity. She aims to seduce, not shock. She'd rather show, say, ants crawling on a dead girl's fingers. The ants were a piece of exposition in the screenplay, written by retired DEA agent Don Ferrarone, who based the story on his real-life experiences investigating homicides in Texas. “It's such a specific detail,” Mann says. “It could only have been something he'd seen.”

Ants. The shape of a lamp shade. The color of a person's eyes. A shadow. “I feel like that's how people remember traumatic events. Little inconsequential details,” she adds. “Because we can't absorb the full impact of the trauma.”

Beneath Texas Killing Fields' gritty police procedural beats the eerie heart of a ghost story. Ghosts are the manifestation of things we keep hidden, Mann believes. The voices we can't shut off in our heads. “At the morgue I remember thinking, 'There's a whole novel inside each of those bodies,' ” she says. “Those stories, they're the reason why I'm here.”

It was sensory information she was after, rote protocol, sounds and smells as much as sights. Visceral knowledge, like the fact that when you step out of the morgue into fresh air, you don't exactly leave the bodies behind. Your clothes still reek of them. “If you're a cop, you do that every day.”

She learned that part of the job is honing your relationship with death. “Not only that, but you need to have a relationship with your reaction to death. You need to quickly become familiar with how you cope, so you can manage it.”

On the premise that the only way an artist can convey a real experience is to experience reality, Mann talks of a “mandate of authenticity.” Part of the mandate is to deliver a convincing verisimilitude. The other part “is to understand the grays.” To refrain from assigning value judgments to characters, even to the bad guys: Society is as responsible for creating the situations that create bad guys as it is for catching them.

Although she's had the privilege of watching both her father, Michael Mann, and Robert Redford work (she was the latter's intern and video assistant on A River Runs Through It), she doesn't exactly know how other directors do it — whether they funnel their made-up universes fully intact from some deep inner well, or airlift them from reality, as she does, one painstaking piece at a time. This is simply the way she's worked out for herself.

Mann's only criteria in taking on projects: Can she sink herself into the world? Does she want to hang out in it for a while? Whether mass audiences do remains to be seen. Early reviews of Texas Killing Fields have been mixed. “Some said it's too police-procedural,” she says, looking thoughtful. Perhaps she did the job she set out to do too well.

LA Weekly