DOWNTOWN BROOKLYN - The teen gunman accused of shooting and critically wounding a livery cab passenger over the weekend faced a judge today. Police say Michael Magnan, 19, attempted to rob the driver while his cab was stopped on Utica Avenue Saturday night. The driver punched Magnan in the face, prompting him to draw a weapon and fire a shot into the cab. He missed the driver and hit the passenger, Nikita Grebelsky, 23. Grebelsky was reportedly left brain dead. Police say Magnan is suspected in two other violent incidents over the weekend. They say he may have been involved in a shooting on nearby East 54th Street, where four people were wounded at a family gathering. Investigators are also looking into whether the teen is connected to an incident at a nearby club, where bouncers were pistol-whipped. Magnan is expected to return to cort on Wednesday.