Two men were ordered held without bail today after they pleaded not guilty to charges that they shot and killed a Roxbury man Thursday night at the Dudley MBTA station, an attack that prosecutors said was recorded on MBTA surveillance cameras.

Brian Cooper, 25, and Jamel Bannister, 22, were arraigned at Roxbury Municipal Court on murder and firearms charges, as well as charges of being armed career criminals. The victim was identified as 26-year-old Courtney Jackson.

In court, Suffolk Assistant District Attorney David Fredette told Judge David Poole that Cooper and Bannister were at Dudley Station, a major public transit hub in Roxbury, around 9:50 p.m. Thursday.

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MBTA surveillance cameras in the station and on an MBTA bus captured the crime as it happened, Fredette said. He said the two men are shown having some interaction with Jackson. Then, Cooper can be seen pulling out a firearm and shooting Jackson, while Bannister stands nearby, armed with his own handgun.

“It is about as callous, cowardly and brazen an incident as I’ve seen in my time doing this job,” said Fredette. “This defendant pointed a gun not only at the victim in this case, but at a crowd of people who were just waiting to get on the bus at 9:45 on a Thursday night.”

John Tardiff, an attorney representing Cooper, told the judge, “Certainly, I want to assert now, that my client is not one of the duo that was present at that scene. He is not that second man.”

Police are still investigating the motive for the attack, authorities said.

Boston police working a paid detail at the station heard the gunfire and arrested both men within a minute of Jackson’s murder, according to a police report. Police recovered two handguns at the station, officials have said.

In a report filed in court, police said they were charging Cooper with being an armed career criminal because he had been convicted of violent crimes in Essex Superior Court in 2007 and Clinton District Court in 2009. In 2007, he was convicted of unlawful possession of a firearm in Boston Municipal Court.

Brian Cooper (l) and Jamel Bannister (r) (Boston Police)

Bannister is also charged as an armed career criminal due to a 2008 unlawful possession of a firearm conviction in Dorchester Municipal Court and a 2010 conviction in the same courthouse for assault and battery on a police officer, according to the report.

Darrin Lally, 36, of Roxbury said he was in the area to get a slice of pizza and asked construction workers about the heavy police presence when he arrived. He said the workers told him they saw police arrest the two suspects, and they also heard the shots.

“They heard two,” Lally said at the scene. “Pow, pow.”