The office building in San Bernardino, California, where 14 people were massacred last month, reopened on Monday.
Security would be heightened for the facility, which was closed in the aftermath of the Dec. 2 shooting, said Inland Regional Center Executive Director Lavinia Johnson.
The property would remain fenced off, and guards at each entrance would continue to monitor security, Johnson said. The San Bernardino attack was the worst incident of gun violence in the U.S. since the December 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut.
Syed Rizwan Farook and his wife, Tashfeen Malik, stormed into a holiday party attended by his co-workers from a San Bernardino County social services agency and opened fire on Dec. 2, killing 14 people and wounding 22 others.
Authorities have said the couple was radicalized over several years.
The couple attacked the California holiday party just weeks after gunmen and suicide bombers linked to the Islamic State in Iraq and the Levant (ISIL) killed 130 people in a series of coordinated attacks in Paris on Nov. 13.
The San Bernardino attackers had not targeted any of the center's roughly 600 staff members, but rather employees of the San Bernardino County Department of Public Health, Johnson told reporters Monday.
None of the people with developmental disabilities that the center serves would visit this week, the Los Angeles Times reported. Many of the center's employees have continued to work and visited their clients' homes over the past month. But they hadn't been together in the place since law enforcement officers whisked them away after the gunfire.
A former neighbor of Farook's, Enrique Marquez, who allegedly bought the assault rifles used by the couple in the San Bernardino massacre has been charged with terrorism-related counts including conspiring with Farook to commit terrorist attacks in 2011 and 2012 that they never carried out. Marquez was Farook's next-door neighbor and longtime friend who converted to Islam and was radicalized by Farook, federal prosecutors said.
Al Jazeera with wire services