Fans gather at a memorial for Kobe Bryant near Staples Center on Monday in Los Angeles. Bryant, the 18-time NBA All-Star who won five championships and became one of the greatest basketball players of his generation during a 20-year career with the Los Angeles Lakers, died in a helicopter crash Sunday.

CALABASAS, Calif. — The pilot of the helicopter that crashed into a hillside outside Los Angeles, killing former NBA superstar Kobe Bryant and eight others, told air traffic controllers in his last radio message that he was climbing to avoid a cloud layer, said an accident investigator on Monday.

The pilot had asked for and received special clearance to fly in heavy fog just minutes before Sunday’s crash and was flying at 1400 feet when he went south and then west, said Jennifer Homendy of the National Transportation Safety Board, which went to the crash scene Monday to collect evidence.

The pilot then asked for air traffic controllers to provide “flight following” aide but was told the craft was too low, Homendy said.

About four minutes later, “the pilot advised they were climbing to avoid a cloud layer,” she said. “When ATC asked what the pilot planned to do, there was no reply. Radar data indicates the helicopter climbed to 2,300 feet and then began a left descending turn. Last radar contact was around 9:45 a.m. and is consistent with the accident location.

Coroner’s officials worked to recover victims’ remains Monday from the hillside outside Los Angeles where the helicopter crashed. Aviation experts say the pilot may have become disoriented in the fog.

While the cause of the tragedy is under investigation by the National Transportation Safety Board, some experts raised questions of whether the helicopter should have even been flying. The weather was so foggy that the Los Angeles Police Department and the county sheriff’s department had grounded their own choppers.

The Sikorsky S-76 went down Sunday morning, killing the retired athlete along with his 13-year-old daughter Gianna and everyone else aboard and scattering debris over an area the size of a football field.

Crews recovered three bodies on Sunday and resumed the effort on Monday amid an outpouring of grief and shock around the world over the loss of the basketball great who helped lead the Los Angeles Lakers to five NBA titles during his dazzling 20-year career.

The pilot was identified as Ara Zobayan. Several aviation experts said it is not uncommon for helicopter pilots to be given such permission, though some thought it unusual that it would be granted in airspace as busy as that over Los Angeles.

But Kurt Deetz, who flew for Bryant dozens of times in the same chopper that went down, said permission is often granted in the area. “It happened all the time in the winter months in LA,” Deetz said. “You get fog.”

The helicopter left Santa Ana in Orange County, south of Los Angeles, shortly after 9 a.m., heading north and then west. Bryant was believed to be headed for his youth sports academy in nearby Thousand Oaks, which was holding a basketball tournament Sunday in which Bryant’s daughter, known as Gigi, was competing.

Bryant had been known since his playing days for taking helicopters instead of braving the notoriously snarled Los Angeles traffic. “I’m not going into LA without the Mamba chopper,” he joked on “Jimmy Kimmel Live” in a 2018 interview, referring to his own nickname, Black Mamba.

Among those killed in the crash were John Altobelli, 56, longtime head coach of Southern California’s Orange Coast College baseball team; his wife, Keri; and daughter, Alyssa, who played on the same basketball team as Bryant’s daughter; and Christina Mauser, a girls’ basketball coach at a Southern California elementary school.