Investigators are calling a Marietta fire at an obstetrics and gynecology office arson, and the FBI has released photos of a possible witness.

The fire started Wednesday at a clinic in the Governor’s Ridge office complex on Powers Ferry Road, which is regularly frequented by anti-abortion protesters. Employees said they saw suspicious activity before the fire.

Clinic workers believe the fire started on the third floor. They said two unknown men went upstairs and left shortly afterward, minutes before the fire was discovered.

“We have patients here. They’re under anesthesia. This could have been life-threatening,” employee Angela Buckner told Channel 2’s Ross Cavitt.

The building was evacuated, and Cobb County firefighters quickly extinguished the flames, but the third-floor was severely damaged, and the lower floors were damaged by water.

The owner of the Marietta clinic is well-known abortion provider Dr. Daniel McBrayer.

The incident came on the heels of another suspicious fire at Atlanta GYN-OB, P.C. in Lilburn. Federal investigators are looking into both fires, but authorities said they don’t know whether they are connected.