Prosecutors say 30-year-old Edward Williams was convicted of murder, kidnapping and other charges in July. A second man was convicted in September and is awaiting sentencing.
Nassau County District Attorney Kathleen Rice says Williams and his accomplice tried to rob a Woodmere man and a friend in June 2010.
During the robbery attempt, the victims were bound and duct-taped and taken inside a home. They were later moved to a car, where one of the victims escaped.
As the victim was fleeing, prosecutors say, Williams shot him in the back.
The victim, 20-year-old Tristan Theodore, collapsed in a neighbor's backyard. He later died at a hospital.