Tarae Lamont Mosby, 29, was arrested on a weapons charge by the Morningside Police Department around 1 a.m. on Sunday.
Investigators say Mosby was arrested while driving his grandmother's car in Maryland. They say he stopped an officer to ask for directions to California.
"When he was pulled over the officer noticed some weapons and ammunition that he should not have been in possession of and that's what originally landed him in jail," Fayetteville Police Spokesman Dan Grubb said. "That actually happened about eight or nine hours before we discovered the bodies here in Fayetteville."
Mosby, who had recently moved to Fayetteville from the Baltimore area, is charged with first-degree murder and larceny of a motor vehicle.
Detectives say he murdered Karen Mosby, 47 and Betty Pettigrew, 69, at their home in the 6000 block of Brookshire Road early Sunday and then took his grandmother's car.
The pair was found brutally murder in their bedrooms inside their home.
"The Medical Examiner has indeed confirmed that the two victims here on Brookshire Road were actually shot," Grubb said.
Investigators have spent the past two days processing the crime scene. They gathered bags of evidence in and outside the home.
Mosby was being held on $10,000 bond in Maryland on the weapons charge, but that will change once he is extradited back to Fayetteville. He will have no bond when he's charged with two counts of first-degree murder.
While Mosby is behind bars the search is still on for a motive, which may be connected to the death of the suspect's sister 11 years ago.
"Back in 1999 there was a car crash involving Mr. Mosby and his sister, where his sister was killed," Grubb said. "He was actually airlifted to a hospital back then. Of course that was about 10 or 11 years ago. How that relates to this case I'm not sure."
But sources close to the investigation tell ABC11 Eyewitness News that part of the suspect's family disowned him after the accident that killed his sister. Now investigators are trying to determine if the internal family rift motivated Mosby to kill his mother and grandmother.