Police say Kieran Smith, of Kings Park, was driving on Express Drive South just east of the Sagtikos Parkway in Brentwood when he got a flat tire.
Smith was walking on Express Drive South when he was struck by a vehicle whose driver fled the scene, according to authorties.
Police say a passing motorist spotted Smith's body on the shoulder and called police at about 7:45 a.m. Sunday.
Smith's family says he was a focused young man, finishing up at Suffolk Community College and laying out his plans to go to medical school.
"Please come forward," his sister Kaitlyn said. "How can you live with yourself? You killed my brother."
She hopes the person responsible will look into her eyes, feel the pain her family is suffering and turn himself or herself in to police.
"They didn't find him for three hours. He lied there for hours," Kaitlyn said. "I can't grasp it. I don't understand it. I don't understand why this happened."
Anyone with information is asked to Crime Stoppers at 1-800-220-TIPS.
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