It has now been 20 years since TWA Flight 800 exploded in mid-air just 12 minutes after taking off from New York's John F. Kennedy Airport en route to Paris, and many are still questioning just what caused the crash that killed all 230 people on board.

The National Transportation Safety Board spent four years looking into the cause in what would become the lengthiest and most expensive investigation in the history of American aviation before publishing their findings in 2000, which stated the explosion was likely caused by a short circuit in the plane's fuel tank.

That scenario seemed implausible however to many, including numerous eyewitnesses who saw the crash from on the ground in Long Island, and in his new book TWA 800: The Crash, the Cover-Up, and the Conspiracy author Jack Cashill takes a look at some of the alternate theories.

The most common is that some sort of missile or rocket hit the plane, and that there was a government cover-up to keep what really happened a secret.

That strike to the outside of the plane may have come from a terrorist or even a US Navy ship according to conspiracy theorists, claims that were both declared untrue by the FBI a little over a year after the crash.

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Tragedy: It has been 20 years since TWA Flight 800 crashed off the coast of Long Island 12 minutes after taking off from JFK Airport in New York City ( the plane being reassembled)

Gone: All 230 people on board the flight, headed to Paris, died in the explosion (wreckage floating in the Atlantic above)

Crash: The National Transportation Safety Board spent four years looking into the cause and declared it to be a short circuit in the plane's fuel tank

Flight 800 was a Boeing 747-131 that had completed over 16,000 flights and been in operation for 25 years when it departed on the evening of July 17 from New York City.

The plane exploded and crashed into the ocean just after 8:30pm as it made its ascent to 15,000 feet eight miles off the coast of East Moriches in the town of Brookhaven, located just west of the Hamptons.

Some who had seen the explosion and crash immediately took action to see if they could find any survivors, including an Air National Guard helicopter that was only miles away and even a few narby residents who were out on the ocean on boats.

The helicopter was eventually forced to turn away due to debris from the plane that was still falling from the sky, while those who approached the burning wreckage in boats said that the smoke was so bad it became impossible to breathe or get close to the scene.

Recovery of the bodies began the next day, a task that took 10 months before all 230 victims were identified.

Wreckage also began being removed from the water soon after, with investigators piecing the plane back together in hopes of getting some idea as to what happened to the doomed aircraft.

The best information at first came from the witnesses who saw the crash, and many told the same exact story of seeing something shoot up towards the plane just before the explosion.

Of the 755 individuals that the FBI spoke with who witnessed some aspect of the crash, at least 258 described seeing a streak of light prior to the plane's explosion while close to 100 said that they watched that streak travel from the Earth up towards the aircraft.

Different story: Of the 755 eyewitness who spoke to the FBI, 258 described seeing a streak of light heading towards the plane before the explosion (wreckage loaded on to a flatbed above)

Putting it back together: Cashill speaks with eyewitnesses again and those who have never spoken before who believe they saw a rocket or missile

Allegations: He also examines claims of a possible government cover-up involving the FBI and CIA

Cashill spoke to some of these witnesses for his new book, including the woman considered by many to be one of the most crucial people the FBI interviewed after the crash, Witness 73.

The woman's identity has never been revealed, but she is one of the few people who was closely watching the plane when the explosion occurred.

She had been visiting friends when she decided to go down to the beach around 8:30pm, just before the explosion brought down the aircraft.

The FBI report stated in its summary of her interview: 'While keeping her eyes on the aircraft she observed a "red streak" moving up from the ground toward the aircraft at an approximately a 45 degree angle. The "red streak" was leaving a light gray colored smoke trail. The "red streak" went passed [sic] the right side and above the aircraft before arcing back toward the aircraft’s right wing.'

Witness 73 described the streak as looking like 'an upside down NIKE swoosh logo.'

She continued to watch as the streak connect with the plane according to the report, which said: 'She then observed a fire at the aircraft followed by one or two secondary explosions which had a deeper sound.

'She then observed the front of the aircraft separate from the back. She then observed burning pieces of debris falling from the aircraft.'

Cashill uncovers shocking new information in speaking with Witness 73 for his new book though, including claims that someone inside a government agency may have attempted to discredit her statement by falsifying records.

Scary: One woman known as Witness 73 described the streak that hit the plane as looking like 'an upside down NIKE swoosh logo.'

Reenactment: The angle which the plane was seen as falling out in a CIA animation was questioned by some eyewitnesses

All the pieces: It took 10 months to identify all the bodies of the dead, which had to be retrieved from the water

Cashill also revisits interviews he did with eyewitnesses from his 2001 documentary on the same subject, Silenced: TWA 800 and the Subversion of Justice.

Among those he spoke to were Mike Wire, who was building a bridge in nearby Westhampton at the time of the explosion.

Wire said in the documentary that he watched a white light as it 'zig zagged' from the beach up in the air before it 'arched over' and disappeared from his view.

Seconds later he saw 'an orange light that appeared to be a fireball' and heard four loud explosions as the plane fell from the sky.

He was only interviewed once however, and even that is not as shocking as the story of David McClaine.

McClaine submitted a report about what he saw almost immediately after the crash as he was a pilot flying from Boston to Trenton going in for a landing when he watched the aircraft explode right in front of him.

In his new book TWA 800: The Crash, the Cover-Up, and the Conspiracy (above) author Jack Cashill takes a look at some of the alternate crash theories

Cashill reveals in his book however that despite the vantage point, the fact that he was more familiar with planes than any other eyewitness and that he was the first to actually report the explosion he was not interviewed by the National Transportation Safety Board until 1999, three years after the crash.

Meanwhile, the CIA’s Deputy Director for Intelligence released a statement about the crash in 1997, saying: 'Our analysis demonstrates that the eyewitness sightings of greatest concern to us – the ones originally interpreted to be of a possible missile attack – took place after the first of several explosions aboard the aircraft … combined with the total absence of physical evidence of a missile attack, [this] leads CIA analysts to conclude that no such attack occurred.'

The findings by the CIA and FBI do not add up however to Cashill, as he explores in his book.

"'The single greatest structural cause for the September 11th problem was the 'wall' that segregated or separated criminal investigators and intelligence agents,” Attorney General John Ashcroft told the 9-11 Commission in April 2004,"' Cashill told DailyMail.com.

'Thanks to a treasure trove of recently unearthed CIA documents we now know that the FBI and CIA ignored the "wall" and collaborated from day one of the TWA 800 investigation. The CIA had no other role but to discredit the 258 FBI witnesses to a missile strike.

'Overseeing the TWA 800 investigation was deputy attorney general Jamie Gorelick. In 1995, Gorelick wrote the wall memo. In 2004, Gorelick sat on the 9-11 Commission.