MARIETTA, Ga. -- An apartment complex security guard was shot and killed Saturday morning by an off-duty Atlanta police officer, after the guard awoke the officer and his wife by banging on the couple's door.

Investigators said 37-year-old Xavier Mallet of Marietta worked as a security guard for the Ivy Ridge apartment complex located at 2650 Bentley Road in Marietta.

For reasons unknown, authorities said Mallet awoke the couple as they slept in their apartment by banging on their door around 4:30 a.m. Investigators said when the female resident answered the door, the 37-year-old security guard forced his way into the apartment.

Within moments, investigators said the female's husband, 36-year-old John Kevin Freeman, an off-duty Atlanta police officer, confronted the security guard. Investigators said the guard was unarmed.

Investigators said Freeman's wife fled the apartment. The security guard and off-duty officer also stepped outside, where investigators said a second confrontation took place. Investigators said Mr. Freeman reentered the apartment and retrieved a firearm. After doing so, investigators said Freeman shot and killed the security guard as the guard was leaving the area.

When authorities arrived at the scene, they found the security guard lying in the front parking lot of building six deceased from gunshot wounds.

Cobb County detectives have since charged John Freeman with murder and aggravated assault. He is currently being held without bond at the Cobb County Adult Detention Center.

Freeman is a 6-year veteran of the Atlanta police department.