What they found Thursday, however, suggested that her boyfriend of 10 years had pulled the trigger intentionally.
Jamie Edward McCook, 31, now sits in the Burke County jail on a charge of malice murder. His father, Ralph McCook, also has been charged in connection with the shooting.
The McCooks told authorities Tuesday that Jamie McCook had been handling his weapon between 4 and 4:30 p.m. at Ralph McCook's home in the 200 block of Greiner Circle when the .40-caliber handgun misfired and hit his 29-year-old girlfriend in the abdomen.
"The medical examiner said it could not have happened that way," Sheriff Greg Coursey said.
An autopsy Thursday revealed that Brown suffered a contact wound.
"What that means is that the gun was pressed against her flesh when it was fired," Coursey said. "(Jamie) McCook stated the gun went off when he was sitting across the room, but according to the medical examiner, the gun was pressed against her abdomen."
Coursey said Jamie and Ralph McCook have continued to stick with their original explanation of the shooting.
On Thursday, however, officers upgraded Jamie McCook's previous charge of involuntary manslaughter to malice murder. He is also charged with possession of a firearm by a convicted felon and possession of a firearm during the commission of a crime.
Ralph McCook was booked Friday into the Burke County jail on a charge of giving false statements to law enforcement.
"We're comfortable that it was intentional, but we don't know a motive at this time," Coursey said Friday.
Coursey said he is unaware of any domestic violence between the Augusta couple. Jamie McCook, though, is on probation for felony marijuana charges in Richmond County.
The Georgia Bureau of Investigation is assisting the Burke County Sheriff's Office in the case.