LEXINGTON COUNTY, SC (WACH) - Authorities arrested a Maryland man accused of killing his girlfriend by shooting her in the back of the head on Sunday.

According to Lexington County Sheriff James R. Metts, Genesis Matthew Pearson, 22, of Baltimore was arrested by detectives with the department on charges of murder and possessing a weapon during the commission of a violent crime.

Arrest warrants allege that Pearson shot his live-in girlfriend, Alishia Monique Dorsey, 21, in the back of the head around 2 a.m. Sunday while the couple was traveling from Maryland to pick up their 13-month-old son, who was staying with relatives of Pearson.

Metts says the motive and circumstances of the shooting remain under investigation. Pearson and Dorsey had been romantically involved for about for years. Their child had been staying with Pearson's aunt and uncle for approximately two weeks. Pearson was driving car before the incident.

Officers responded to the call concerning the shooting Sunday morning and found Dorsey lying on her back in the road in front of the home of Pearson's aunt and uncle. Pearson was standing outside of the home with blood on his shorts and shoes; he was not wearing a shirt.

According to the department, a 9mm handgun and a bloody shirt was discovered in a grassy area near Leaphart Road.

Lexington County Coroner Harry O. Harman ruled that Dorsey's death was a homicide. A forensic pathologist determined that Dorsey died within minutes after suffering a gunshot wound to her head. 

The investigation is ongoing.