EAST ELMHURST — Officials said they have begun an investigation into the death of Noel Polanco, the 22-year-old man who police shot dead on the Grand Central Parkway after an early Thursday morning traffic stop. Authorities said Polanco was driving erratically, dodging in and out of traffic, speeding and cutting off two police trucks and an emergency service unit. When the two responding officers stopped him, authorities said the officers believed Polanco was reaching for a weapon when they saw him reach under his seat.