One reason is because police have had difficulty finding all the bullets while combing through acres of land.
RELATED: Gilroy Garlic Festival shooting survivors share harrowing tale after being released from hospital
The festival happened in a wooded area and a bullet from an assault rifle can travel two miles.
The 19-year-old gunman who opened fire was "kind of a loner" and much of his life was shrouded in mystery, an FBI official said as investigators searched for a motive.
Police believe Santino William Legan fired randomly after cutting through a fence to get into the annual Northern California food festival. Officers patrolling the popular event responded within a minute and killed him.
Get the latest on the deadly Gilroy Garlic Festival shooting here.