(CNN) -- An unreleased documentary on the 1996 TWA Flight 800 explosion offers "solid proof that there was an external detonation," its co-producer said Wednesday.

"Of course, everyone knows about the eyewitness statements, but we also have corroborating information from the radar data, and the radar data shows a(n) asymmetric explosion coming out of that plane -- something that didn't happen in the official theory," Tom Stalcup told CNN's "New Day."

A number of people have come forward, "all saying the same thing: that there was an external force -- not from the center wing tank, there's no evidence of that -- but there is evidence of an external explosion that brought down that plane," Stalcup said.

He cited "corroborating information from the radar data" and complained that "not one single eyewitness was allowed to testify -- that's unheard of."

Photos: TWA Flight 800

The film's producers are submitting a petition -- signed by "many" former investigators -- asking for the National Transportation Safety Board to reopen its investigation, based on new evidence offered by the documentary, Stalcup said.

"The family members need to know what happened to their loved ones," he said.

Asked why such information might have been suppressed, he said, "That's a question that should be answered when this investigation gets reopened."

The NTSB ruled that the explosion was caused by an electrical short circuit, most likely originating in a fuel gauge line, which found its way into the center wing fuel tank, where it detonated fuel vapors and caused the B-747 to fall in pieces into the waters off Long Island.

Skeptics have long theorized that TWA Flight 800 was brought down by sinister forces.

They include Hank Hughes, who served as a senior accident investigator with the NTSB and helped reconstruct the aircraft. Others include Bob Young, a TWA investigator who participated in the investigation, and Jim Speer, an accident investigator for the Airline Pilots Association.

"These investigators were not allowed to speak to the public or refute any comments made by their superiors and/or NTSB and FBI officials about their work at the time of the official investigation," a news release announcing the documentary said.

"They waited until after retirement to reveal how the official conclusion by the (NTSB) was falsified and lay out their case."

The documentary, "TWA Flight 800," will premiere July 17, the 17th anniversary of the crash.

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