(CNN) - Millions of people never met him, but the sudden death of Kobe Bryant and eight others has left a country in mourning.
The 41-year-old NBA legend died in a helicopter crash under foggy conditions in Calabasas, California. Visibility was so low Sunday morning that Los Angeles police had grounded its helicopters, spokesman Josh Rubenstein said.
The helicopter crashed into a hillside, killing all nine people on board -- including Bryant's 13-year-old daughter, Gianna. The official cause of the crash has not been determined.
As fans around the world grapple with Bryant's death, new clues are emerging about what happened shortly before the crash.
The helicopter was operating under "special visual flight rules" (SVFR), according to an air traffic control conversation with the pilot, captured by website LiveATC.net.
An SVFR clearance allows a pilot to fly in weather conditions worse than those allowed for regular visual flight rules (VFR).
Pilots can request SVFR clearance before takeoff or mid-flight, especially if conditions suddenly change, CNN transportation analyst Peter Goelz said.
While SVFR clearance is "pretty normal," he said, "it's not something that's often recommended."
"If you're a pilot, and you're in marginal conditions, or changing conditions that become marginal, you might call air traffic control" to request SVFR, Goelz said.
If granted SVFR clearance, the pilot will typically keep tighter communication with air traffic control.
The Burbank Airport control tower allowed the helicopter to proceed using the special clearance, the audio reveals.
"Maintain special VFR at or below 2,500" the pilot confirmed to the controller.
Later in the flight, the pilot apparently asked for "flight following," a service in which controllers are in regular contract with an aircraft.
The controller told the pilot "you're still too low level for flight following at this time." That could mean the helicopter was too low to be seen on air traffic control radar.
While authorities try to determine what went wrong, investigators are struggling to find clues in difficult conditions.
"It's a logistical nightmare in a sense because the crash site itself is not easily accessible," Los Angeles County Sheriff Alex Villanueva said.
The effort to recover the victims' bodies has started but could take days, given the terrain and the condition of the site, Los Angeles County Chief Medical Examiner Jonathan Lucas said.
Children and parents were on board
Bryant was traveling to a basketball game with Gianna, who was scheduled to play Sunday afternoon.
hey were joined by Orange Coast College (OCC) baseball coach John Altobelli, his wife Keri and his daughter Alyssa, Altobelli's brother told CNN.
Alyssa was Gianna's teammate, OCC assistant coach Ron La Ruffa said. And Altobelli would routinely travel with his daughter for her basketball games.
OCC President Angelica Suarez said she was devastated by the loss of "a member of our OCC family."
"Coach Altobelli was a giant on our campus -- a beloved teacher, coach, colleague and friend," Suarez said in a statement. "This is a tremendous loss for our campus community."
Another parent, Christina Mauser, was also killed in the crash. Mauser was an assistant girls basketball coach for a private school in Corona del Mar, California.
"My kids and I are devastated. We lost our beautiful wife and mom today in a helicopter crash," her husband Matt Mauser wrote on Facebook.
Fog blanketed the area
The crash occurred under foggy and cloudy conditions with extremely low visibility, CNN meteorologist Michael Guy said.
Pictures taken shortly after the crash showed the density of the fog.
Witnesses said the helicopter plummeted quickly before crashing on the hillside, Los Angeles County fire Capt. Tony Imbrenda said.
It was not immediately clear whether the Sikorsky S-76B helicopter radioed a distress signal, Imbrenda said.
Local authorities are working with the National Transportation Safety Board and Federal Aviation Administration to try to determine the cause of the crash.
Sikorsky, the helicopter manufacturer, tweeted its condolences.
"We extend our sincerest condolences to all those affected by today's Sikorsky S-76B accident in Calabasas, California," the company said.
"We have been in contact with the NTSB and stand ready to provide assistance and support to the investigative authorities ... Safety is our top priority; if there are any actionable findings from the investigation, we will inform our S-76 customers."
The helicopter was built in 1991 and was most recently registered to Island Express Holding Corp., according to the FAA.
Calls to Island Express were not answered Sunday.
A nation in shock and mourning
Devastated fans flooded an area near the crash site as well as Staples Center in Los Angeles, the city where Bryant spent his entire 20-year NBA career.
Born in Philadelphia, Bryant quickly soared to become one of basketball's greatest champions. He won five NBA championships, before retiring in April 2016, capping his career by scoring 60 points in his final game.
Former Lakers Coach Phil Jackson called Bryant a "chosen one -- special in many ways to many people."
Bryant is survived by his wife, Vanessa, and his three other daughters -- the youngest of which was born in June.
CNN's Aaron Cooper, Artemis Moshtaghian, Chloe Melas, Chuck Johnston, Darran Simon and Jon Passantino contributed to this report.