TWA Flight 800: What's still unknown

• 230 people were on board TWA Flight 800 from 13 countries


• The government spent four years and millions of dollars in the investigation


• The FBI said the disaster was not caused by a terrorist act

Watch at 9 p.m. ET Tuesday, July 15, for a CNN Special Report, "Witnessed: The Crash of TWA Flight 800."

(CNN) -- On July 17, 1996, TWA Flight 800 took off from JFK Airport headed for Paris. Just 12 minutes later, it exploded over the shores of Long Island, New York. There were 230 people on board, and no one survived.

Accident investigators said Wednesday, July 2, they would not re-open the probe of the mid-air explosion that brought down TWA 800 nearly 18 years ago on July 26, 1996, killing all aboard. The decision by the National Transportation Safety Board dashed the hopes of a documentary film team claiming to have uncovered "solid proof" that investigators erred in concluding it was an accident. Here, a section of the wing of TWA Flight 800, seen here a couple of days after the crash, floats in the Atlantic Ocean off Long Island, New York.

A member of the U.S. Coast Guard pulls a piece of wreckage from the waters on July 18, 1996.

Ron Dwyer pauses to compose himself on July 20, 1996, as he speaks about his 11-year-old daughter Larkyn Lynn Dwyer, who was on TWA Flight 800.

A warning sign on the dunes alerts beach-goers to watch for debris washed ashore at Smith's Point, Long Island, New York, on July 25, 1996.

A police officer stands guard as part of the plane is transported from a dock in Brooklyn, New York, on July 19, 1996.

Wreckage of the front portion of the Boeing 747 aircraft is displayed in its reconstructed state on November 19, 1997, in Calverton, Long Island, New York.

Parts of the aircraft's wing sit in the hangar on July 8, 1999, in Calverton, New York.

The partially reconstructed fuselage of TWA Flight 800 is pulled out of a hangar in Calverton, New York, on September 14, 1999.

Antonella Naglieri, whose relatives Giuseppe Mercurio and Anna D'Alessandro were killed in the crash, places a rose in the surf after a memorial service at Smith Point Park in Shirley, New York, on July 17, 2001.

Joanne Festa touches the memorial wall commemorating the victims of TWA Flight 800 on July 16, 2006, at the Smith Point County Park in Shirley, New York.

TWA Flight 800

Many eyewitnesses described seeing something heading toward the plane before it exploded, and the suspicion of terrorism was almost instant. The biggest investigation in aviation history, at that time, ensued.

The government spent four years and millions of dollars in that investigation and 18 years later, many still question whether they got it right.

With that in mind, here are five surprising things you probably didn't know about the investigation, including one big thing the investigators themselves still don't know:

1. The FBI interviewed at least 755 witnesses.

TWA Flight 800 crashed eight miles off the coast of Long Island at dusk on a clear summer night. Hundreds of witnesses saw the plane explode from either on shore, on a boat, in a plane or in at least one case, a helicopter.

Of the 755 witness reports that the FBI have made public, accounts vary widely but hundreds describe what they thought was either a flare or fireworks heading up toward the plane before it exploded. A few witnesses even used the words "missile" or "rocket."

2. America was in a high state of alert when TWA 800 crashed.

A series of terrorism-related events in the years, months and weeks before the flight went down, and even one incident just days afterward, led many to suspect terrorism was to blame.

Clockwise from top left: Convicted Lockerbie bomber Abdel Baset Ali Mohmed al Megrahi (1992), World Trade Center garage (1993), Atlanta Centennial Olympic Park (1996), Federal Building in Oklahoma City (1995).

-- December 21, 1988: Pan Am Flight 103 explodes over Lockerbie, Scotland, killing all 270 people on board. Eventually Libyan national Abdel Baset Ali Mohmed al Megrah is tried and found guilty of 270 counts of murder.

-- February 26, 1993: A bomb explodes at the World Trade Center, killing six people and injuring more than 1000. Two years later, Ramzi Yousef, the mastermind of that attack, is arrested in Pakistan by the FBI and the State Department and put on trial. "I am a terrorist and proud of it," he told the court.

-- April 19, 1995: The Alfred P. Murrah building in Oklahoma City is bombed. The blast destroys large parts of the building and kills 168 people, including 19 children. Two Americans, Timothy J. McVeigh and Terry L. Nichols, are eventually convicted for the attack.

-- May 29, 1996: Yousef goes on trial in New York City. The trial continues through the crash of TWA Flight 800, leading many to question if the two were related.

-- June 25, 1996: The Khobar Towers are attacked. A powerful truck bomb explodes on the perimeter of a U.S. military complex in eastern Saudi Arabia. Nineteen U.S. Air Force personnel are killed, and several hundred are wounded, in the deadliest attack against the American military since a 1983 bombing of the Marine headquarters in Beirut, Lebanon.

-- July 17, 1996: TWA Flight 800 explodes over the shores of Long Island.

-- July 27, 1996: A bomb explodes at the Olympic Games in Atlanta, killing one person and injuring over 100. More than two years later, Eric Robert Rudolph, a suspect in bombings at abortion clinics in Alabama, is charged in the Olympic Park bombing.

Covering the crash: One CNN reporter remembers

3. Moammar Gadhafi and Saddam Hussein were suspects.

Beyond terrorist groups being suspected, state-sponsored terrorism was also cause for concern inside the White House. Leon Panetta, former secretary of Defense and former CIA director, was chief of staff for President Bill Clinton at the time of the crash.

"The investigation was looking at almost every possibility, including state actors, because we'd known that Libya had been involved with regards to bringing down the airliner over Scotland (Pam Am Flight 103)", said Panetta. "We were looking at Iraq and Saddam Hussein. We were looking at, you know, the possibility of even Iran might have played a role in this," added Panetta.

4. It took close to a year, but all 230 victims were eventually recovered.

There were 230 people on board TWA Flight 800 from 13 countries. When the plane crashed into the water, much of what was left sunk 130 feet below the surface in the Atlantic Ocean.

While it took authorities more than 10 months, remains of every victim were recovered. All of their names are etched into the TWA Flight 800 International Memorial at Smith Point County Park on Long Island, New York. The memorial was dedicated on July 14, 2004, and it includes flags from the 13 countries of the victims.

5. The NTSB said a spark in a fuel tank led to the explosion

In November 1997, more than a year after the crash, the FBI announced that a criminal act did not bring down the ill-fated plane. At that point, it was up to the National Transportation Safety Board to figure out the cause of the explosion.

A full four years after the crash of TWA Flight 800, the NTSB released its official report: It found the probable cause of the accident was a spark in the center fuel tank that eventually led to the explosion that brought down the aircraft. While they offered their best theory on where the spark came from, they never found a definitive answer.

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