The seven-man military jury deliberated four hours before reaching the verdict in the trial of Capt. Richard Ashby.
He showed no emotion when the verdict was announced, but his mother, Carol Anderson, cried out, "Oh, no! Oh, no!" and began crying quietly.
A sentencing hearing was scheduled to begin Friday afternoon. He could receive up to 10 years in prison, or be dismissed from the Marines.
In closing arguments Thursday, a prosecutor said Ashby intended to impede an investigation into the tragedy when he took the videotape from his damaged jet.
"Who in this situation had the most to gain to make sure there wasn't any information about this flight?" Maj. Daniel Daugherty said. "He handed over that tape knowing it was going to be destroyed."
The 32-year-old Marine pilot doesn't deny removing the tape filmed by his navigator. His lawyer, Frank Spinner, said Ashby had no criminal intent but had "exercised poor judgment."
Ashby, of Mission Viejo, Calif., was the pilot of a EA-6B Prowler that severed a ski gondola cable near Cavalese, Italy, on Feb. 3, 1998, causing the 20 people aboard to plunge more than 350 feet to their deaths.
His acquittal on manslaughter charges in March outraged Italians and renewed calls to ban Americans from NATO air bases in Italy.
After the jet landed, Ashby put the tape in his flight suit pocket. He retrieved it a few days later, wanting to see what was on it, he testified, but couldn't find a video player and handed it over to the navigator, Capt. Joseph Schweitzer, 31.
Schweitzer said he later threw the tape into a bonfire, and he pleaded guilty to the charges that Ashby was convicted of Friday. He was sentenced to dismissal from the Marines.
Schweitzer said he feared that the tape, which included shots of the flight before the accident and images of his face, would be played in the Italian media with scenes of the carnage.
Prosecutors said Ashby and Schweitzer's actions showed calculating, criminal intent to mislead investigators.
"They knew when they brought a $50 million aircraft back badly damaged there was going to be an investigation," Daugherty said. "Without that tape, there's a lot of speculation. Without that tape, we'll never know for sure what went on in that cockpit."
Two back seat crewmen in the radar-jamming aircraft were charged after the accident. Those charges were dismissed last year.