The 18-year-old was the former co-captain of both the Connetquot High School football and lacrosse teams.
Connetquot High School football coach Mike Hansen says Hartnett was planning to attend Briarcliffe College in the fall.
Police say Hartnett was driving on Ocean Avenue in Ronkonkoma when he lost control of his car and struck a tree and a porch about 3:40 a.m. Tuesday.
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