The crosses were created by retired Chicago carpenter Greg Zanis, who also made 58 crosses in honor of the Las Vegas mass shooting victims.
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Thousand Oaks shooting: Remembering the victims
The 12 crosses were placed just outside the Borderline Bar & Grill. The crosses have the names of all 12 victims killed in the mass shooting.
The crosses make up part of a makeshift memorial outside the nightclub. Area resident Michelle Kam-Biron came out to the memorial to pay her respects Monday morning.
She said she read about the crosses on a Facebook post.
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"I was just touched that someone from across the country could feel the pain that we're feeling here in Thousand Oaks," Kam-Biron said. "That he sacrificed all that time and trouble and made all these crosses for these victims of such a tragic and terrible event that happened - it was just touching, and that's what brought me out here."
Kam-Biron described the massacre as "senseless."
"The guns...I don't want to get into politics, but it's terrible, losing one's life over such a senseless act," Kam-Biron said.
PHOTOS: Mass shooting at nightclub in Thousand Oaks, California