CCTV has revealed that Spencer Stone was stabbed from behind during a brawl near a bar in Sacramento.
First Class Airman Stone, 23, was stabbed four times after an altercation in a nightclub led to a confrontation in a street.
The footage appears to show Stone knocking a man to the ground before he is stabbed from behind.
Deputy Chief Ken Bernard of Sacramento Police said two suspects, described as Asian males in white T-shirts and blue jeans, fled the scene in a late-model Toyota Camry, NBC News reported.
The incident has not been treated as related to terrorism or Stone's involvement in thwarting an attack by gunman Ayoub El Khazzani on a train to Paris in August.