The Gate Fire, which started Saturday morning and quickly spread to 1,500 acres is now a criminal investigation, Cal Fire confirmed Sunday.
All evacuation orders were lifted early Monday and the blaze was 95 percent contained after scorching more than 3 square miles of dry brush near Jamul, the state Department of Forestry and Fire Protection said.
Investigators spoke to a witness who posted an Instagram video that appears to show people starting the fire.
The people seen in the video are not being considered suspects or persons of interests at this time because it's not known if they did anything criminal, Cal Fire spokesperson Isaac Sanchez said.
The man who recorded the video was cooperating with the investigation, Sanchez said.
Investigators do not know if an illegal weapon was used prior to the fire or if the fire was manually started, he said.
Officials would not confirm if they had any suspects or any other details of the investigation.
Cal Fire investigators and Bureau of Land Management are handling the investigation.