The Black Forest fire started in a wooded area and investigators have found no obvious signs of accelerants used at the scene, the El Paso County Sheriff's Office said on Wednesday.
While the cause hasn't been determined investigators have made "great progress" and gathered "many items of evidence" and other information, the Sheriff's Office said in a release.
The release said investigators are looking at a number of possibilities, including mechanical sources such as sparks from machinery or hot components on motors, the release said.
The human-caused fire started on June 11 and burned 14,280 acres, killed two people and destroyed at least 511 homes. It was contained on June 20.
"Much of the information and evidence has been obtained through numerous interviews, processing the area of origin, and the execution of multiple search warrants," the sheriff's office said in a press release.
"Search warrants can be valuable in propelling a case forward, but are equally helpful in ruling out properties or people within the scope of an investigation as well. Any investigative activities seen at a single home does not mean it is a home or area of stronger interest than any other," the release states.
The sheriff's office said specific details about the evidence and search warrants won't be released "in the interest of the integrity of the investigation."
The U.S. Forest Service, Colorado Bureau of Investigation, the Bureau of Alcohol, Tobacco and Firearms and the Aurora Fire Department are assisting in the investigation, the release said.
Anyone with information about the cause of the fire should call the tip line at 444-8393 or email firstname.lastname@example.org.
Contact Daniel ChacOn: 476-1623 Twitter @danieljchacon Facebook Daniel Chacon