Raymond Mong, who died in the bus crash, pleaded guilty to the Connecticut hit-and-run, records show. View Full Caption DNAinfo/Trevor Kapp and Connecticut State Police

QUEENS — The private bus driver who plowed through a red light and collided with an MTA bus Monday — killing himself and two others — was working illegally for his company after a 2015 drunk-driving crash, officials said.

Raymond Mong, 49, died Monday when his bus owned by the Dahlia Group, which has a long history of deadly crashes and negligence, crashed into a MTA Q20 bus and killed two others, Henry Wdowiak and Gregory Liljefors, officials said.

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The charter bus company were required by state law to notify the DMV that he was driving for them, following his 2015 arrest, according to spokeswoman Tiffany Portzer.

"This is an ongoing state and federal investigation and we cannot comment further," Portzer said.

In a preliminary investigation, the National Transportation Safety Board found Mong was traveling between 54 and 62 miles per hour at the time of the crash, lead investigator Robert Accetta said Tuesday.

Police on Tuesday said they're still investigating the crash and couldn't say what caused it. The NTSB is also continuing its probe, and it could take days to gather more information on what caused the crash, Accetta said.

Mong has a history of bad driving, having pleaded guilty to an April 10, 2015, drunk driving crash in Connecticut, according to Connecticut State Police.

Mong was drunk while driving a Honda Accord along Interstate-95 in East Haven when he rear-ended a Volkswagen Jetta driven by a 22-year-old woman with man, 25, in her passenger seat, police records show.

The Jetta then slammed into a Chevy Tahoe driven by a 56-year-old man, police said.

Mong fled the scene in his car, but was later arrested and charged with DUI, according to police and court records.

He pleaded guilty, served six months in jail and was given 18 months probation, records show.

"We made a decision based on the evidence that that would be in his best interest," said Mong's attorney at the time, Justin Smith, of Connecticut-based Duffy Law.

Mong had also been working for the MTA in 2015, but was fired that year, a spokesman said.

The spokesman didn't provide further details.

Later, Mong started working for the Dahlia Group and was behind the wheel Monday morning when his bus crashed in Flushing, police said.

The impact destroyed the front of the Dahlia bus. Mong, who'd been living in College Point, was pronounced dead at Elmhurst Hospital, police said.

Wdowiak, a 68-year-old from Flushing, was walking along the sidewalk when the buses careened into him, police said. He was pronounced dead at the scene.

Liljefors, who was 49 and also lived in the neighborhood, was aboard the Q20 when the impact spun it around violently, police said. He was pronounced dead at New York-Presbyterian/Queens, police said.

Officials with Dahlia have repeatedly refused to comment after the deadly crash.

Mong's former attorney wouldn't say much about his client, citing attorney-client privilege, but extended his condolences to the victims of Monday's crash.

"It's just a terrible tragedy and my thoughts and prayers go out to the victims in this incident, including his family," Smith said.