As part of a plea deal with Cumberland County prosecutors, Christopher Robinson will also serve five years of supervised release once he's freed. He pleaded guilty last month to murder and attempted kidnapping.
Prosecutors say the 34-year-old Millville man was trying to stuff his girlfriend into the trunk of his car at a convenience store in February 2007 when 51-year-old Carmen DeGregorio intervened.
DeGregorio, who had served on the Millville force, freed the woman and fought off Robinson, who then ran him down in the parking lot.
DeGregorio sustained serious head injuries and died two days later.