According to a report, investigators are analysing a digital photograph, taken by an amateur astronomer from San Francisco, that apparently shows a thunderbolt striking the Columbia space shuttle as it streaked across the California sky seven minutes before crashing, killing all seven astronauts, including Indian American Kalpana Chawla, onboard.

The image is one of five taken at around 0553 hours [local time] on Saturday, it said.

The photographer, who requested anonymity, said he will not release the image to the public until experts from the National Aeronautics and Space Administration have examined it, according to SFGate.com.

On Tuesday NASA sent former astronaut Tammy Jernigan, now a manager at the Lawrence Livermore Laboratories, to the home of the astronomer to examine his images and to take the camera itself to Mountain View, where it was to be transported by a NASA T-38 jet to Houston.

Jernigan questioned the photographer on the aperture of the camera, the direction he faced and the estimated exposure time on the automatic Nikon 880 camera, which was mounted on a tripod.

The report said that in the shot, a purple light corkscrews down toward the plasma trail, appears to pass behind it, then cuts toward it from below. As it merges with the plasma trail, the streak itself brightens for a distance, and then fades.

The Columbia Crash: The Complete Coverage