Brian McHenry is one of the world's foremost experts in automobile accident reconstruction. Back in the '60s, his father created the first reconstruction software, and Brian, 42, joined the family business more than 20 years ago.

CBS News 48 Hours asked McHenry, who lives in North Carolina, to recreate the accident. In conjunction with the Flying Foto Factory, a graphics and animation company, they created a simulation of the accident. (Click on the video clip at left to see the simulation.)

CBS.com talked to McHenry about the art and science of accident reconstruction, and about this case.

The Nuts and Bolts of Accident Reconstruction

"What you do is, you set up a vehicle mathematically. You know the weights of the vehicle, you find out suspension height, and as best you can, the suspension properties, moments of inertia, all the things that basically define the vehicle in a mathematical sense. We set up in the terrain, which is basically the roadway it has to run on. Then you basically drive the car mathematically on the roadway."

Brian McHenry at work.

On His Clientele

"A lot of the work we do is litigation-related. In other words, we're either defending or we will work for a plaintiff. Basically what we do is, we take everything on a case by case basis. Someone comes to us and says 'We've had an accident, can you tell us what happened?' And we tell them... and let them fight it out. That's the easiest way to put it."

A scene from McHenry's reconstruction.

On The Specifics Of This Case

"You normally want to look at the vehicle, which is inaccessible in this case... With this one, what I had to do is, I set up the targets where I knew the car had to run through. And I ran it through at different speeds and then I ran it through into the post, and I tried to find the right amount of speed and residual velocity that it would need to spin to the point of rest."

The Perils Of Eyewitness Accounts

"They've had tests where they take 20 people out and run a crash test, and they ask them a question and they offer you different things. Eyewitnesses -- especially in something this high profile. [In this case], most of the witnesses did not know who was in the collision. They all left. Then they say, 'oh there was a crash and I saw it'. Now, is what they think they saw what they saw, or is it a combination of what they saw and what they saw on TV and heard about, and things like that? The onl thing that we can work with is just the physical evidence. And that's what we worked with -- just the tire marks, the damage to the vehicle, and the position of rest of the vehicle from the point of impact, and of course the terrain it ran over."

For more information on McHenry and accident reconstruction, see his company's Web site.

For more information on the Flying Foto Factory, check out their site.

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interview by David Kohn

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