An 18-year-old man was charged with killing his grandmother Monday after a neighbor saw suspicious activity outside the woman's home and her body was subsequently found in a vehicle the young man was driving, authorities said.

Brandon Machetto is accused of killing 74-year-old Sylvia Rosalie Schmitt after some type of argument at her home in Paradise Lakes, a gated condominium and nudist community. Pasco County Sheriff Chris Nocco said his office was consulting with prosecutors about what level of murder charge Machetto will face.

The grandson had been staying with Schmitt for the last few weeks and had a history of domestic violence, including an arrest in a previous altercation with Schmitt, the sheriff's office said.

Nocco said the sheriff's office received a call from a neighbor around 5:30 a.m. reporting an alarming sight.

"What he saw was Brandon kind of looking around the neighborhood as if he was up to something," Nocco said. "At that time, the neighbor keeps watching Brandon. Brandon then takes a body that’s wrapped up – the neighbor can see feet – he takes (the body) into his minivan and he drives off."

The sheriff's issued a Silver Alert for Schmitt and responded to the home, where deputies found signs of blood and a struggle, Nocco said.

Just after 10 a.m., Deputy Ricky Frisco spotted Machetto driving the van on State Road 54. The deputy tried to pull him over, but Machetto kept driving at about 25 mph until he wound up back in Paradise Lakes and was finally stopped around 50 yards from his grandmother's home.

"Our detectives were there, and we were able to do a takedown on him and put him in custody," Nocco said. "Looking in the back seat, we unfortunately found the body of Sylvia."

Deputies said after being taken into custody, Machetto was stoic and uncooperative, refusing to answer questions and keeping his head down.

Machetto’s old martial arts instructor is surprised.

“I used to see him and his grandmother together all the time, all the time, never a problem. She’d tell him when he was good playing ball, made sure he took his medication, very close,” said Ronnie Hall.

But he said Machetto was very immature and believes it may be because of a brain injury he sustained at age 13. Even with medication, Hall said Brandon had never been the same since.

Authorities said the medical examiner will determine the cause of death.

Nocco said it appears Machetto was living with his grandmother because he had nowhere else to go. Machetto previously had been arrested on burglary and criminal mischief charges.

"It's extremely sad," Nocco said. "Another sad day in Pasco [County] where we are talking about domestic violence again. Unfortunately it takes something like this to bring it into the spotlight."