Garland Andrews captured cell phone video of the bus stuck and the impact that followed between the train and bus.
"People losing their life right in front of you," said Andrews.
He was running to the scene with many others as the horrific scene unfolded.
Andrews said he started recording the stuck bus on the tracks to document what he described as a long time problem. This outcome was the worst he'd ever seen with four dead and dozens injured.
"I prayed and cried and called my mom," said Andrews.
WARNING: Viewer discretion is advised. You may find the video below disturbing. Please note, the video has been edited for explicit language.
Duane McKervey was on the bus with his wife Kim, who is still in the hospital with broken ribs. Coming back to the scene was difficult.
"For me to be out here the next day talking to you about it, there's a higher being," said McKervey.
The NTSB says since 1976, 17 vehicles have collided with trains at the Main Street crossing in downtown Biloxi.
Tuesday's crash was the deadliest.
"Our mission is to not only to find out what happened but why it happened. That's critical. To learn from this so it won't happen again," said NTSB Board Member Robert Sumwalt.
Andrews says he wants to make sure of it.
"Implement something that's going to change what's going on in my city of Biloxi because there's been too much loss of life," said Andrews.
One of the victims killed in Tuesday's bus accident was from the Houston area, officials announced Wednesday.
Two victims were from Lockhart, one from Bastrop and another from Sealy.
The Harrison County coroner confirmed 73-year-old Peggy Hoffman and 82-year-old Kenneth Hoffman, both of Lockhart, died at the scene. Sealy resident 79-year-old Clinton Havran was also killed at the scene.
Lockhart ISD released a statement saying two former administrators, Ken and Peggy Hoffman, were killed in the accident.
Deborah Orr, 62, of Bastrop, died at Merit Health Biloxi Tuesday night after undergoing surgery, according to the coroner.
VIDEO: Bastrop officials give update about Biloxi victims
A freight train smashed into a charter bus in Biloxi, pushing the bus 300 feet down the tracks and leaving at least four people dead, authorities said. Rescuers spent more than an hour removing passengers, cutting through the bus's heavily damaged frame to extract the last two.
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The bus could be seen straddling the tracks, with a CSX Transportation locomotive pushed up against its left side. The bus was apparently stopped on the tracks when the 52-car train, pulled by three locomotives, slammed into it, said Biloxi Police Chief John Miller.
"We're not sure why," Miller said. "We don't know if there were mechanical issues or what was taking place."
Miller said passengers on the Echo Transportation bus had come from Austin, Texas, carrying passengers to one of Biloxi's eight casinos. Ameet Patel, senior vice president of regional operations for Penn National Gaming, owner of Hollywood Gulf Coast Casino in Bay St. Louis and Boomtown Biloxi Casino, said the bus was traveling from the Hollywood casino to the Boomtown casino at the time of the crash.
"It's a terrible tragedy," Miller said. "I know there's a lot of families that are going to be impacted here."
The bus was carrying more than 50 passengers affiliated with a senior citizens group from Bastrop, Texas. Margaret Atkins, president of the group, explained the bus became stuck on the tracks.
RAW VIDEO: Press update from Bastrop group
"The bus driver realized they were not going to be able to get off the tracks in time, so he opened the front the doors and allowed some of the members to get out that way," she said. "Others got out of the back doors. Unfortunately, the others that were in the middle were the ones that were injured."
There were conflicting reports of the number killed in the crash. Officials initially said four people died and then revised it down to three. But Vincent Creel, a spokesman for the city of Biloxi, later said after consulting with the coroner's office that four were killed.
Creel emphasized it's a "very fluid situation."
"Any time you have a major incident like this, the information can change," he said.
Michelle Crowley of the Biloxi fire department said 40 people were injured; of those, seven were in critical condition.
A woman who lives about a block from where the train and bus finally came to a stop after the train crashed into the bus says she heard a "loud boom" and knew immediately what had happened.
Cecelia McDonald said she ran out of her house and saw a scene of carnage.
Witnesses told the Sun Herald of Biloxi that the bus was stuck on the tracks for about five minutes before he saw the train hit it. Mark Robinson said some people were getting off the bus as the driver tried to move it, and at least one person was shoved under the bus when the train hit. A nearby car was used as a stepladder after the crash to get people off the bus, and emergency workers pulled passengers through windows.
Robinson said he thinks the train track, which is on an embankment, poses safety issues.
In addition to bells, warning lights and crossing arms, the crossing has yellow signs warning drivers that it has low ground clearance.
"It's too steep there," Robinson said.
Biloxi Fire Chief Joe Boney says rescuers needed one hour and four minutes to clear everyone from the wreckage. Two people had to be cut out of the bus.
Creel, the city spokesman, said 48 passengers and the driver were on the bus; a bus manifest had listed 50 passengers but two of them did not make the trip.
Medical workers from a hospital blocks away set up a triage area at the scene, and helicopters carried some of the passengers to other hospitals.
The train was headed from New Orleans to Mobile, Alabama, at the time of the crash, said CSX spokesman Gary Sease. He said the train crew was not injured. The single track is the CSX mainline along the Gulf Coast, passing through densely populated areas of southern Mississippi.
Federal Railroad Agency records show 10 trains a day typically use the track, with a maximum speed of 45 mph. Records show there have been 16 accidents at the crossing since 1976, including in 1983 and 2003, each of which involved one fatality. A delivery truck was also struck at the same crossing in January, WLOX-TV reports. No one was injured in that crash.
The bus was marked as belonging to Echo Transportation, which Texas corporate records show is a unit of a company called TBL Group, based in Grand Prairie, near Dallas.
"We can't confirm anything at this point," said Elisa Fox, a lawyer for the bus company. "We're trying to mobilize to assess the situation."
Federal Railroad Administration spokesman Marc Willis said the agency is sending three inspectors to investigate, while Mississippi is sending one. The National Transportation Safety Board said it is also investigating.
The Associated Press contributed to this report.