A 17-year-old in Brevard County, Fla., was arrested Friday on suspicion he ambushed a 46-year-old grandmother and shot her dead in a friend's driveway, according to Local 6 News.

Investigators said Christy Sanford was shot at about 10:50 p.m. Tuesday along the 1200 block of A Street in Cocoa, Fla.

Police arrived within minutes of the shooting and found Sanford dead, still sitting in her car with the driver's door open and the headlights on.

After an investigation, police identified Clarence Tarez Thomas as the alleged shooter, Local 6 News reported.

Thomas' family was contacted by detectives, and the teen turned himself in to police Friday.

Police said they are not sure why what appeared to be a robbery turned to murder, according to the report.

"In a lot of these cases, what happens is that people do reflex things out of anger or whatever," Cocoa Police Chief Phil Ludoz said.

Investigators said Thomas is a high school dropout with an extensive criminal record.

"He has been known in the community as carrying weapons in the city and committing crimes that have not been reported," Cocoa Detective Pat Dovl said.

Sanford, a Canaveral Groves grandmother studying to be a paramedic, was visiting a friend to pick up an injured rottweiler mix named Diamond when she was shot and killed.

Thomas faces a first-degree murder charge in connection with the shooting.

Watch Local 6 News for more on this story.