(People) A witness has spoken to PEOPLE about the stabbing assault on Spencer Stone that took place Thursday on the streets of Sacramento – leaving the French train attack hero in hospital with serious injuries.
While doctors say Stone is expected to make a full recovery, authorities are continuing to piece together what led to the attack.
Eric Cain, who works at a liquor store near the scene of the fight, says Stone behaved heroically as tried to help a girl in trouble moments before he was stabbed.
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"A big group was walking down the street and they went into the intersection," Cain tells PEOPLE. "One of the guys hit one of the girls and the guy who turned out to be Spencer Stone went after that guy. It happened really quickly."