More than 200 workers at the Inland Regional Center, a complex in San Bernardino, stood with their heads bowed to mark a moment of silence punctuated by the bell tones.
Many of the same people were at their jobs on December 2, 2015, when married couple Syed Rizwan Farook, 28, and Tashfeen Malik, 29, opened fire in a conference building at the complex during a holiday party and training session for San Bernardino County employees, who were Farook's co-workers.
It was one of the deadliest acts of violence by militants in the United States since the September 11, 2001, hijacked plane attacks. Twenty-two people were also wounded in San Bernardino.
"It's a day that marked all of our lives, it destroyed some lives, it destroyed families," Zen Martinsen, 56, a county worker whose friend lost a niece in the shooting, told reporters after the ceremony. Martinsen worked at a different office.
The ceremony outside the large conference building, which has sat empty behind a chain link fence since the shooting, was one of a day-long series of events in San Bernardino.
A private ceremony was organised for family members of victims and survivors of the attack, according to San Bernardino County spokesman David Wert.
"Somebody that would take hate and internalize it to such a degree that they felt that they were going to do something that would promote their agenda at the expense of so many innocent people, I was certainly saddened by that," San Bernardino Mayor R Carey Davis said on Friday.
FBI investigators are still seeking to answer key questions, such as the location of the married couple's computer hard drive.
In another symbolic act on Friday, dozen of bicyclists, including many police officers, participated in a bicycle ride of 14 miles (23 km), one mile for each person killed.
In the evening, another San Bernardino event was expected to draw at least 2,000 participants to an arena.
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