Bus driver in deadly New York crash was fired by MTA after DUI was discovered The crash was between a New York City transit bus and a Dahlia charter bus.

 -- The driver of a tour bus who was killed in a Monday morning bus crash in New York City that left two others dead was a former New York Metropolitan Transit Authority (MTA) employee who was fired for cause in 2015 when it was discovered he had been arrested for driving under the influence, the MTA said.

This morning’s fiery crash was captured on stunning surveillance video, which shows the moment when a Dahlia charter bus barreled into the MTA bus at one of the most densely packed intersections in Queens in New York City.

The crash left three people dead and 19 others injured, according to the MTA. Four of those injured are in critical condition, the MTA said Monday evening.

In the video, provided to ABC News by ABC station WABC in New York, the MTA bus is seen turning a corner in Flushing just after 6:15 a.m. when the Dahlia bus crashes into it. The crash sent the charter bus onto the sidewalk and into a restaurant, sparking a small fire, officials said. The fire was quickly put out by firefighters, who treated the injured.

The charter bus' speedometer was photographed at the scene stuck at 60 mph — twice the speed limit in the intersection. While investigators have not determined why the bus was apparently going that fast, sources said investigators have recovered enough surveillance video to conclude the charter bus was speeding when it crossed the intersection.

Raymond Mong, who died in the crash, was the driver of the tour bus that slammed into the MTA bus. The MTA began the process of firing Mong in 2015 after learning he was arrested for driving under the influence in New Haven, Conn., sources familiar with the investigation tell ABC News. At some point after, he was hired by Dahlia.

Connecticut state police confirm that Mong was indeed arrested for drunk driving in April 2015 after causing a pileup on the off-ramp of a highway. Mong "fled the scene," but was later located and arrested, police records show.

The New York State Department of Motor Vehicles was notified of the DUI and informed the MTA, which began the grievance process, according to sources familiar with the investigation. Mong was pulled from the road and fired by the MTA soon after.

On Monday, New York Mayor Bill de Blasio said, "It's just shocking to see the scene."

"It's hard to compare it to anything I've seen — the sheer destruction from the impact of this collision," he said.

"We want to make sure we understand exactly what happened and prevent this from ever happening again," said Joe Lhota, the chairman of the MTA.

In addition to Mong, those killed were a passenger on the MTA bus and a passer-by who was run over, according to officials. Sources briefed on the investigation said the victims were Mong, 49; the passenger Gregory Liljefors, 55; and the pedestrian, Henry Wdowiak, 68.

The MTA bus driver, a 10-year veteran, is in a hospital in noncritical condition. He is being interviewed about the collision.

According to federal records, Dahlia has been cited multiple times for speeding violations. Because of its history of violations, Dahlia was prioritized by federal officials for more frequent unannounced inspections, said an official from the Federal Motor Carrier Safety Administration.

The National Transportation Safety Board is sending a team to investigate the crash.

ABC News' Erin Dooley contributed to this report.