Journalist alleges cover-up in 1966 death at Doris Duke's Rough Point mansion

The death of a designer at Doris Duke's Rough Point mansion in Newport in 1966 was ruled an accident.

But an author now says Duke got away with murder because she had help.

The official account states that Duke mistook the brake for the gas and accidentally pinned Eduardo Tirella against the gates of her Newport mansion.

But author Peter Lance says forensic evidence he uncovered shows what really happened.

"If you look at the official death certificate, all of his internal injuries are upper body. But all of the injuries, damage to the gate, are below his waist. So, she could not have crushed him against the gates," Lance said.

There's more: "There was no trail of blood, no blood on the gates, no trail of blood from the gates into the street, but Officer Angel saw in the middle of Bellevue Avenue or about a third of the way into Bellevue Avenue, found blood and skin."

Is it plausible for someone to jump on the hood of an oncoming car?

Lance says yes.

"It's an actual phenomena that people, to avoid being killed by vehicles, jump up on the hood. So, he most likely (is) staring at her through the windshield, terrified. She bursts through these gates, bends the gates, and then taps the brakes for a second, a moment of hesitation, just outside the gates, whereupon his body rolls off," Lance said.

Is this speculation?

"I don't know what was in her head, I'll just tell you this: She decided to commit. If she had not done that, had she gotten out of the car -- 'Oh, Eduardo, what can I do? Let's call the police. Let's call the rescue wagon!' -- he would have been living. OK? But she decided to roll over him, and she dragged him across Bellevue Avenue," said Lance.

According to Collision and Injury Dynamics, the single sequence would imply, in most cases, an accident. A multi-sequence event is affirmative decisions that lead to the conclusion that, in this case, according to Lance, Doris Duke did this on purpose?

Lance said, "Absolutely. The conclusion is unmistakable. Doris Duke conspired with the Newport Police Department to get herself out of criminal charges. They left out that key element of rolling up on the hood because they would have to arrest her on the spot. They would have to put those handcuffs on her that day, they would have had to."

Lance accuses Duke's attorney Aram Arabian and then-Newport Police Chief Joseph Radice of conspiring in a cover-up.

Radice retired seven months after the crash and died in 1997.

"They conspired to create a fabricated three-page phony question-and-answer transcript of an interrogation that never took place. I found that transcript after I uncovered the police report, which had been missing since at least 1990," Lance said.

NBC 10 News reached out to the Newport Police Department for a response but have not heard back.

The story doesn't end there. In my next report, why Eduardo Tirella's family says he was killed twice.

Watch additional segments in this series:

Part 1: Journalist takes new look at 1966 car crash death at Doris Duke's Rough Point

Part 2: Journalist argues death of Doris Duke's friend at Rough Point was no 'unfortunate accident'

Part 3: Journalist alleges cover-up in 1966 death at Doris Duke's Rough Point mansion

Part 4: Journalist claims police helped Doris Duke escape accountability for death at Rough Point

Web Extra: 'NBC 10 Biographies' tells life story of heiress Doris Duke