(CBS) A sequence of five government photos shows the moment the hijacked American Airlines plane slammed into the Pentagon last Sept. 11.

The photos were taken by a surveillance camera positioned north of the section of the Pentagon destroyed by the impact and the resulting explosion and fire.

The images cover a span of four one-hundredths of a second. The first photo shows a small, blurry white object near the upper right corner — possibly the plane just a few feet above the ground. The second shows a white glow immediately after the impact. In the three remaining photos, a mountain of orange fire and black smoke rises above the building.

The photographs were not officially released by the Pentagon, but officials said the images were authentic and had been provided to law enforcement officials investigating the attack. The photographs were obtained by CBS News and other news organizations Thursday.

Officials could not immediately explain why the date typed near the bottom of each photograph is Sept. 12 and the time is written as 5:37 p.m. The attack happened at about 9:37 a.m. on Sept. 11. Officials said it was possible that the date and time were added the day after the attack when they may have been catalogued for investigative purposes.

Meanwhile, workers are rebuilding the Pentagon so quickly that by Sept. 11, U.S. Defense Department employees will be working at the same spot where the crash happened.

"We want them sitting at their desks, doing their work" on the anniversary of the attack, said Walker Lee Evey, program manager of the restoration project.

The back-in-business symbolism of that image inspires hundreds of workers laboring long hours to restore the Pentagon's western flank and the offices inside. So far, the project is months ahead of schedule, Evey said.

"They have tremendous motivation," Evey said Thursday. "Some lost family members" in the crash.

"The Phoenix Project" is already rising fast, but Evey is careful to say that the work will be far from finished by the tragedy's anniversary.

Unlike the outermost "E Ring," home to the offices of the most senior Defense Department employees, the "C" and "D" rings that also were damaged will likely not be completed by Sept. 11, he said.

That could happen as early as next year, when the new facade will blend seamlessly with the original, near an outdoor memorial planned by the Army Corps of Engineers.

Evidence of recovery has edged out signs of disaster.

Gone from the western flank is the jagged hole of blackened concrete ripped open by a rogue jetliner traveling 350 mph, six feet above the ground. In its place is a 100-yard-wide rectangular gap partly filled with five stories of floors in various states of construction. Looming overhead are two 140-foot-tall cranes.

Pentagon officials did not predict such quick progress given the damage and the unique challenges facing rebuilders of the massive building.

American Airlines Flight 77 and its 20,000 gallons of fuel spread destruction, fire and death, killing 189 people in the plane and on the ground.

The fire was so hot, Evey said, that it turned window glass to liquid and sent it spilling down walls into puddles on the ground. The impact cracked massive concrete columns far beyond the impact site, destabilizing a broader section of the building than contractors had originally thought.

Several challenges confronted the contractors. Poisonous mold in kaleidoscopic colors climbed the interior walls, fed by millions of gallons of water that had been sprayed at the fire over two days. Gloved, gas-masked workers pumped hot, dry air through the windows to remove it.

New security measures — from fortifying the structure's windows and walls to improving air flow, sprinklers and escape routes drove up the price from around $700 million to about $740 million, Evey said.

Of the 4,600 Pentagon workers who were displaced by the attack, some 1,500 are back in their offices while others work elsewhere in the Pentagon or in rented space.