The wreckage of the helicopter that crashed in the hills of Southern California last month, killing basketball legend Kobe Bryant, his 13-year-old daughter and seven other people showed no outward sign of engine failure, the National Transportation Safety Board (NTSB) said Friday.

Bryant, 41, his daughter, Gianna, and the other passengers and pilot died in the Jan. 26 crash when the Sikorsky S-76B helicopter they traveling in went down in the Los Angeles suburb of Calabasas. They were on their way to a girls basketball tournament in which Gianna Bryant was playing.

The NTSB is investigating whether fog, among other variables, played a factor in the accident, the agency said in an investigative update. The helicopter's instrument panel was destroyed in the crash and most devices were displaced from their panel mounts, it said.

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Because a tree branch near the crash site appeared to be cut, investigators believe the engine was working and the rotors were working during impact. The update said a witness told investigators that he saw the helicopter flying one of two seconds before it crashed. He said it was flying forward and in a downward direction.

The helicopter was not equipped with a flight data recorder and cockpit voice recorder nor was it required to be, the NTSB said.

In addition, the aircraft did not have a terrain awareness and warning system. which gives a signal when an aircraft is in danger of hitting the ground. The NTSB has recommended the system be mandatory for helicopters but the Federal Aviation Administration (FAA) only requires it for air ambulances.

Sen. Dianne Feinstein, D-Calif, is demanding all commercial helicopters be fitted with terrain awareness and warning systems. In 2006, the NTSB recommended to the FAA that all helicopters that carry six or more passengers be required to have the technology.

Ara Zobayan, 50, the pilot for the Island Express-owned helicopter, had a reported 8,200 hours of flying experience. He was also a pilot to other celebrities, including Los Angeles Clippers player Kawhi Leonard and Kylie Jenner.

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Island Express announced days after the crash that it was "suspending all flight service for operational reasons." No details were provided.

Bryant, a 14-time All-Star, played 20 seasons for the Los Angeles Lakers, winning five NBA championships. Memorials and tributes have spanned the city and throughout the sports world, including the Super Bowl.

A public memorial will be held at the Staples Center in downtown Los Angeles on Feb. 24. The date is significant, as it corresponds to Bryant's No. 24 jersey and the No. 2 worn by Gianna.

Items placed in front of the arena in remembrance of the beloved NBA star were removed Monday. Bryant's wife, Vanessa, has request some of them be given to his family.

A public memorial will be held for other crash victims, including Orange Coast College baseball coach John Altobelli, his wife, Keri, and daughter Alyssa on Monday at Angel Stadium in Anaheim.

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Zobayan, Christina Mauser, Sarah Chester and her daughter Payton were also killed in the crash. A final report on the crash isn't expected for at least a year.

The Associated Press contributed to this report. This is a developing story, check back for more updates.