PUEBLO, Colo. -- Federal aviation investigators returned to the wreckage of a corporate jet at dawn Thursday to try to determine what caused the plane to crash in freezing drizzle, killing all eight people on board.

National Transportation Safety Board spokeswoman Lauren Peduzzi said investigators recovered the cockpit voice recorder from the twin-jet Cessna Citation C-560 and were sending it to a lab in Washington for analysis.

A warning of icing conditions had been issued and the pilot of an identical plane that landed shortly after the accident reported light to moderate icing, said Frank Hilldrup, chief investigator with the National Transportation Safety Board.

Hilldrup did not elaborate on what NTSB chairwoman Ellen Engleman Connors said were "interesting characteristics" in radar data.

"The descent profile of the plane looked OK, " Hilldrup said, of radar data that showed the plane's altitude at 5 second intervals before the crash.

Earlier, Connors also declined to offer specifics but said investigators are looking for additional radar data. She said they are also reviewing the weather and the possibility of mechanical problems.

Investigators also planned to speak to air traffic controllers at Pueblo Memorial Airport about any communication they had with the crew of the plane, which was preparing to land when it went down on a sagebrush-dotted ranch five miles east of the airport Wednesday morning.

The tower staff declined to release any information to the media.

Meanwhile, the Federal Aviation Administration planned a safety meeting for Friday in Washington to look at corporate jets and on-demand charters. Spokeswoman Laura Brown said the meeting had been scheduled before the Pueblo crash.

"It's a meeting to talk about industry best practices," she said.

Two witnesses told investigators they heard loud popping noises from plane -- owned by electronics retailer Circuit City -- shortly before the crash at about 9 a.m., Pueblo County Sheriff Dan Corsentino said. The cause of the crash was unknown.

Corsentino said an FBI team had visited the site because it is next to the Pueblo Chemical Depot, where aging mustard gas canisters and other chemical weapons are stored. But he said there was no indication of terrorism.

The victims included a pilot, co-pilot and six passengers, Corsentino said. None of them have been officially identified, although the family of Kyle Harmon of Richmond, Va., confirmed Thursday that Harmon died in the crash. He was an employee of Circuit City.

The flight originated in Richmond, home of Circuit City Inc. FAA spokesman Mike Fergus said Pueblo was the plane's destination, but Corsentino said the aircraft was stopping to refuel before heading to John Wayne Airport in Irvine, Calif.

The second company plane, also a Cessna Citation C-560, landed safely about 5 minutes after the crash, and had flown over the burning wreckage.

None of the eight people aboard the second plane spoke with reporters Wednesday. They were visibly shaken and traumatized, the sheriff's department said.

The planes made a refueling stop early Wednesday in Columbia, Mo., Peduzzi said. Randy Clark, general manager of Central Missouri Aviation at Columbia Regional Airport, said Thursday his staff had serviced the plane that crashed but he did not know whether the flight crew mentioned any problems.

"Yesterday was a day of profound sadness as eight members of the Circuit City family and our extended family -- four associates, two partners and two pilots -- lost their lives in a plane crash. Our first priority yesterday was to contact their families; and out of respect for their privacy, we have decided not to publicly release the names," the company said Thursday in a public release. "We have all been touched by the outpouring of sympathy from our associates, friends, the Richmond community and from people all over the country. I want to thank everyone for their thoughts and prayers during this time."

Circuit City will hold a memorial service later this week for its employees. Grief counselors are at the Circuit City headquarters in Richmond helping employees Thursday.

Investigators set up a generator as night fell. The victims' bodies were removed from the scene and sent to a local funeral home until arrangements could be made to transport them to their families.

Fergus said the pilot was relying on the plane's instruments to make the airport approach because of the poor weather. The National Weather Service reported low clouds, fog and freezing drizzle with visibility of about six miles at the airport at the time of the crash. The temperature was 27 degrees.

Aviation analyst John Nance said freezing drizzle is risky because it makes it easy for ice to form on the wings, which adds weight and can affect handling of the plane.

"You can overwhelm almost any airplane, even a 747 if you get into certain types of icing," said Nance, a pilot and author based in Seattle.

"When things get cold and the weather gets tough, some of the margins of safety we inherently have when the sun is shining and the runway is dry and the weather is clear begin to diminish," he said.

In 1998, the FAA required operators of several Cessna models, including the one that crashed Wednesday, to add a warning to their flight manuals that flying in freezing drizzle and other conditions "may result in ice build-up on protected surfaces exceeding the capability of the ice protection system."

The investigation into the cause of the crash is expected to last one year.