The Gilroy Garlic Festival draws tens of thousands each year, and like many large events, there are security checks at the entrance.
Police said the man who opened fire at the festival Sunday, killing three and wounding 15, was able to get around security by entering through a back area of Christmas Hill Park.
Gilroy Police Chief Scott Smithee said the gunman used "some sort of tool" to cut a fence next to a creek to get into the event.
Christmas Hill Park backs up against a wilderness area, though it is unclear exactly where the gunman entered.
Smithee said the festival had security checkpoints with metal detectors.
Taylor Pellegrini, 25, said that her bag was checked at the entrance but that one of her friend's was not.
Founded in 1979, the Gilroy Garlic Festival bills itself as "the world's greatest summer food festival." The three-day event is hosted by community volunteers and raises money for local schools, charities and nonprofit organizations.
The festival attracts tens of thousands of people every year to the Santa Clara County town of 58,000.
"It is such a sad, just horribly upsetting circumstance that this happened on the third and final day of the festival," Brian Bowe, the executive director of the Gilroy Garlic Festival, said at a Sunday night news conference. "And to have seen this event end this way this day is just one of the most tragic and sad things I have ever had to see."
