A wildfire may leave behind acres of blackened ground. But for investigators, the scene is anything but a blank slate.

The clues are still there, hidden in charred trees, bent grass, burnt objects and even the way a pine cone was scorched.

Think of it as a crime scene where the evidence can disappear with the next rain, wind gust or bulldozer pass.

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So how do investigators figure out where a wildfire started, and, more importantly, what caused it?

Jeff Wiedow, Assistant Fire Management Officer with South Dakota Wildland Fire, has spent the last 41 years learning how to do exactly that. And while he says he wouldn't call himself a detective, the work sounds remarkably similar.

“You follow the science, and that will tell you where the fire started," Wiedow says.

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(MORE: See the new technology that stops wildfires before they begin)

Gathering the evidence

When Wiedow gets called to a fire, he starts by talking to the incident commander.

He wants to know: Were there witnesses? What did they see? Where do firefighters believe the fire started?

Then he walks the perimeter.

Because he's right-handed, Wiedow says he starts on the right and works counterclockwise, looking into the fire for indicators. Then he walks clockwise, looking outward at the surrounding fuels.

Wildfire investigators even have their own vocabulary for reading the scene: The head is the direction the fire was moving, while the heel is the opposite end.

That distinction is crucial because investigators generally work backward from the head toward the heel.

Backing fire can be slow, creeping and smoldering, while head fire burns more cleanly and intensely. Those differences leave clues behind.

For a suspected human-caused fire, Wiedow starts in the least-burned area and works back and forth in a zigzag pattern. As the clues begin pointing toward the same location, the search area gets smaller until you reach the ignition area.

(MORE: What it feels like inside a wildfire)

Deciphering the clues

Investigators look for what they call "fire indicators," which are physical clues that reveal the direction and behavior of the flames.

Take a pine cone. If one side is charred while the other remains protected, that difference can reveal which direction the fire traveled.

Once investigators determine where the fire started, the next question is: What caused it?

Wiedow says a lightning-struck tree can have a distinctive spiral burn pattern, whereas human-caused fires can be much less obvious.

“About 70 percent of fires are human-caused,” he says.

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Three of the biggest causes he sees are downed power lines, equipment malfunctions and debris burning.

That's where the investigation can become particularly challenging.

A roadside fire, for example, may have plenty of potential suspects: a vehicle, a cigarette, something thrown from a window, or a trailer dragging a safety chain through dry grass.

You may be able to determine exactly where the fire started, but proving which one of those things actually ignited it can be much harder.

Investigators also have a formal guide for determining wildfire origin and cause. The guide provides a framework for documenting evidence, interpreting fire indicators and working systematically toward a conclusion.

Solving the case

Finding the cause isn't just about closing a case. It can help prevent the next fire.

If investigators discover that escaped debris burns are repeatedly starting wildfires, for example, that information can shape public education and prevention efforts.

“To have a good prevention program, you need a good investigation program,” Wiedow says. “They work hand in hand.”

So investigators walk the blackened landscape, following clues most people would never notice, assembling the puzzle piece by piece.

And if the evidence is good enough, investigators can work backward through the destruction to find the place where the story began.