Fontana Police said that about 2 p.m., three to four suspects entered the swap meet and immediately attacked a security guard, beating him with a gun and a sledgehammer.
After attacking the guard, the suspects went to a jewelry counter and began smashing it. The security guard reportedly shot a round at the suspects, striking one. The others ran away. The suspect hit by gunfire was declared dead at the scene.
No one else was injured. The security guard's condition was not released.
Police are reviewing surveillance video from the scene.