A smoke plume is shown rising from the Fontenelle fire in Wyoming in this July 1, 2012 NASA handout photo obtained by Reuters July 5, 2012.
Denver (Reuters) - Investigators probing the cause of the most destructive wildfire in Colorado history have located the point of ignition but have not concluded how the blaze started, officials said on Thursday.

At its height, the 12-day-old blaze forced the evacuation of some 35,000 people in and around Colorado Springs, the state's second most populous city, and threatened the campus of the U.S. Air Force Academy before fire crews gained an upper hand late last week. It destroyed more than 300 homes and killed two people.

Since it was first reported on June 23, the blaze has burned more than 14,000 acres of drought-parched timber and brush, mostly in the Pike National Forest about 50 miles south of the Denver metropolitan area. But as of Thursday, ground crews had managed to carve containment lines around 90 percent of the fire's perimeter, said incident commander Rich Harvey.

Harvey said he anticipates full containment by late in the week as crews work to extinguish flames in a few stubborn areas. "When there's been no smoke visible and no heat detected for 24 hours, we'll be comfortable there will be no further growth and we'll call it 100 percent contained," Harvey said.

The burn scar from the Waldo Canyon Fire is pictured in this handout photo from an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on the Terra satellite by NASA, in Colorado Springs,Denver taken July 4, 2012

Investigators, led by U.S. Forest Service experts, have identified the spot where the so-called Waldo Canyon fire began. But Lieutenant Jeff Kramer, spokesman for the El Paso County Sheriff's Office, said he was "not at liberty" to reveal the location because the investigation was continuing. "The cause has not yet been determined," he added.

A task force consisting of wildfire specialists from several agencies is taking part in the investigation, including local police and fire departments, the FBI and federal Bureau of Alcohol, Tobacco and Firearms, police in Colorado Springs said in a statement issued on Thursday. The Colorado Springs fire follows a recent string of suspected arson fires in a neighboring county, but officials have said they had no indication that the Waldo Canyon blaze was deliberately set.

"We're still investigating whether this is suspicious," Colorado Springs police spokeswoman Barbara Miller said. The blaze initially gained media attention as it erupted near some of Colorado's best known landmarks, including the famed Pikes Peak mountaintop whose panoramic summit vistas inspired the song "America the Beautiful."

© REUTERS/Adrees Latif
A man, who's house escaped fire damage, walks through his backyard after returning to his Mountain Shadows neighborhood which was devastated by the Waldo Canyon fire in Colorado Springs, Colorado on July 4, 2012.
Stoked by strong, erratic winds and record triple-digit air temperatures, the fire turned deadly last Tuesday as it suddenly roared through containment lines into a residential subdivision that rests in the bluffs of the city's western fringe. The wall of flames reduced 346 houses to ash, marking the biggest single loss of property ever from a Colorado wildfire, and President Barack Obama paid a visit to the Waldo Canyon fire zone last Friday.

The bodies of an elderly couple, William Everett, 74, and his wife, Barbara, 73, were found in the ruins of one home, raising to six the overall death toll from a state fire season authorities are calling the worst on record. Most of the residents displaced by the fire have since been allowed to return to their homes.

Meanwhile, Colorado Springs Police Chief Peter Carey said an anonymous donor has offered a $50,000 reward for information leading to the arrest of anyone who looted the homes of evacuees, following dozens of looting reports.