Jakwan Keller, 20, pleaded guilty to second-degree manslaughter charges back in March.
Twelve-year-old Dejah Joyner was killed in the October 2015 shooting.
Keller was upset that someone from a rival gang had stolen his brother's hoverboard and went looking to retaliate.
When he allegedly shot at Dejah's house in Hempstead, a group of people was standing out front.
Dejah was in the living room of the house and a bullet came through the front window, striking her in the head.
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