Police have arrested one of the suspects they believe is responsible for beating a teenager unconscious last week after attacking him on the L train in Brooklyn. 

A 15 year old boy from Queens was arrested on second-degree robbery charges, police said on Monday. 

The NYPD released two surveillance photos over the weekend of the suspects who allegedly started beating the teen on the L train near Broadway Junction in East New York after asking what gang he was in.

They later dragged him off the train at the Atlantic Avenue stop, stealing his sneakers, pants and cell phone. The victim was treated for a concussion and severe eye injury, police said. 

A bystander took a cell phone video of the attack. 

An NYPD spokesman said police are still looking for three additional suspects, and the department has not confirmed whether the 15 year old arrested is depicted in the photos released by police. 

Anyone with information on the attack is asked to call Crime Stoppers at 800-577-TIPS or submit their tip online.