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Lexington County, SC (WLTX) - Lexington County deputies have arrested a man they say shot and killed his 21-year-old live-in girlfriend as the couple was driving down the road.

Officers arrested 22-year-old Genesis Matthew Pearson on charges of murder and possessing a weapon during the commission of a violent crime.

Officers say around 1:48 a.m. Sunday, Pearson shot Alisha Monique Dorsey in the back of her head in the 2400 block of Leaphart Road near West Columbia. At the time, the two were driving from Maryland toa relative's home here in South Carolinato pick up the couple's 15-month-old son.

Deputies say the woman's body was found lying in the road in front of the relative's house when they arrived. Pearson, officers say, was standing outside thehome.

Officers say they founda gun and a bloody shirt in a grassy area nearby.

According to investigators, the couple had been in a relationship for four years.

The child is now in the custody of his maternal grandmother.