DOWNTOWN BROOKLYN (WABC) -- Police arrested a suspect in the stabbing death of an 18-year-old on the subway last week.
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Officers arrested 25-year-old Mark Smith Tuesday afternoon who was charged with manslaughter and assault.
Officials say a fight broke out on a D train approaching the Atlantic Avenue Barclays Center station Thursday night.
Police say Isiah Collazo from Staten Island was on the train when he and his group of friends got into a dispute with another man on the train.
As the train started moving north out of the station, Collazo was stabbed and the train's emergency brakes were activated. The reason the brakes were activated is still under investigation, but it could have been related to the attack.
The train was already halfway out of the station at the time, and passengers exited through the train cars still on the platform.
Video surveillance recovered by NYPD shows Collazo's four friends dragging him off of the subway train onto the platform, the friends appear to check themselves for injuries and runoff.
The victim initially was transported to the hospital in serious but stable condition, but he died four hours later at the hospital.
One commuter didn't mince words when asked how she felt about police presence.
"Do your damn job...that means you can't be standing up congregating like those behind me, you have to be walking the platform back and forth," she said.
The head of NYC Transit said officer patrol has stepped up and crime is down. Total subway crime fell 8% compared to this time last year.
"We continue to put what we can do in transit, the measures in place, everything from unarmed gate guards to continue to roll out cameras and continue to work very closely with NYPD and MTA police who have been dispatched throughout the system as well," said MTA President Richard Davey. "But by any measure, we are safer. Obviously, that's no solace to the family who lost a loved one last night."