The 19-year-old woman found shot in the head Tuesday morning along a busy Gwinnett highway was the subject of an argument between her alleged assailant and his roommate, authorities said.

Thirty-nine-year-old Edward Samuel Dukes has been charged in the incident, which Gwinnett County police have said started as an argument between him and his roommate at the Madison at River Sound apartments near Lawrenceville. Dukes is accused of pistol-whipping his roommate, who jumped off a second-story balcony to escape while Dukes drove off with the female victim.

Police believe Dukes shot the woman in the head somewhere between the apartments off Walther Boulevard and the exit ramp at Ga. 316 east and Collins Hill Road. Dukes’ car was stopped there, blocking traffic for hours.

The victim was taken to Gwinnett Medical Center and remained there Wednesday in critical condition, Gwinnett County police Cpl. Deon Washington said.

The exact relationship between the woman and the roommates is unclear, as is what, exactly, prompted their argument — but Washington said Wednesday that “apparently the fight between the two men revolved around the girl.”

Dukes remains in the Gwinnett County jail without bond. He is charged with two counts of aggravated assault as well as three counts of possession of controlled substances with the intent to distribute.

The drug charges stem from cocaine, methamphetamine and Xanax allegedly found inside Dukes’ car when he was apprehended. Washington said they were not believed to have played a direct role in the incident.

Domestic incident, shooting blocks Ga. 316 ramp