Check out CNN affiliate KCBS/KCAL in Los Angeles, California.

Los Angeles, California (CNN) -- The Pentagon is unable to explain images of what witnesses took to be a high-altitude rocket launched off the coast of Southern California at sunset Monday, officials said.

But John Pike, a defense expert who is director of GlobalSecurity.org, said he believes he has solved the mystery.

"It's clearly an airplane contrail," Pike said Tuesday afternoon. "It's an optical illusion that looks like it's going up, whereas in reality it's going toward the camera. The tip of the contrail is moving far too slowly to be a rocket. When it's illuminated by the sunset, you can see hundreds of miles of it ... all the way to the horizon.

"Why the government is so badly organized that they can't get somebody out there to explain it and make this story go away. ... I think that's the real story," Pike added. "I mean, it's insane that with all the money we are spending, all these technically competent people, that they can't get somebody out there to explain what is incredibly obvious."

A U.S. Northern Command official who didn't want to be identified said the contrail could very well be from an airplane. An "illusion" effect made the contrail appear as if it's rising straight up, but it's actually level, the official said. The event is similar to another sighting around New Year's Eve in which observers believed they witnessed a missile, he said.

Col. Dave Lapan, a spokesman for the Pentagon, said later Tuesday that while there is no evidence that the contrail was left by a missile the department is still investigating.

No Defense Department units reported launches at the time. The North American Aerospace Defense Command and the U.S. Northern Command did not report any foreign missile launches off the California coast, Lapan added. Regardless, there was no threat to the United States, he said.

Tuesday morning, the Pentagon and the North American Aerospace Defense Command were investigating video shot by a news helicopter operated by CNN affiliate KCBS/KCAL showing an ascending orange-colored contrail high into the atmosphere, officials said. A contrail is the visible vapor trail behind airplanes or rockets traveling at high altitudes.

The Federal Aviation Administration, the Coast Guard, Navy, Air Force, and California Reps. Dana Rohrabacher and Jane Harman -- whose coastal districts are closest to the offshore contrails -- were at a loss to explain the images.

"The FAA ran radar replays of a large area west of Los Angeles based on media reports of the possible missile launch at approximately 5 p.m. (PT) on Monday. The radar replays did not reveal any fast moving, unidentified targets in that area," said FAA spokesman Ian Gregor. "The FAA did not receive reports ... of unusual sightings from pilots who were flying in the area on Monday afternoon.

"The FAA did not approve any commercial space launches around the area Monday," he added.

Lapan said that various agencies are trying to find out what happened.

"I don't know specifically what they are all doing. I just know they have been pinged and that we are talking to the FAA, we are talking to other parts of the U.S. government. We are trying to do everything we can to figure out if anybody has any knowledge of what this event may have been," Lapan said in off-camera comments to journalists.

"So far we have come up empty," he added.

CNN's Charley Keyes and Chris Lawrence contributed to this report.