That’s when a rental truck, containing approximately 5,000 pounds of ammonium nitrate fertilizer, nitro methane, and diesel fuel was detonated in front of the Alfred P. Murrah Federal Building in Oklahoma City, destroying one-third of the building and causing severe damage to several other buildings located nearby. As a result of the massive explosion, 168 people were killed, including 19 children, and more than 800 others were injured. It was the largest terrorist attack on American soil in history before the September 11 attacks. It remains the deadliest act of domestic terrorism in American history.

Fifteen years later, U.S. Department of Homeland Security (DHS) Secretary Janet Napolitano visited Oklahoma City to commemorate the 15th anniversary of the Oklahoma City bombing as part of the Oklahoma City National Memorial Annual Remembrance Ceremony.

Among her remarks at the event: “Today, our first priority remains protecting against, and preventing, another terrorist attack on America. And we have learned from this tragedy by continuing to implement and refine the security standards and procedures developed since 1995.” Earlier this year, the DHS-led Interagency Security Committee announced new security standards for all federal buildings and facilities. And the Federal Protective Service announced the broad deployment of a new risk assessment tool to help their inspectors keep more than 9,000 facilities secure.

Napolitano added, “Terrorism is a tactic designed not just to kill, but to make us feel powerless. But we are never powerless. We control the way we prepare ourselves, the way we anticipate and combat the threats, and the way we respond if something does happen.”

In addition, Secretary Napolitano met with state and local first responders to discuss the importance of close coordination among all levels of government to support frontline emergency response and management efforts. She stressed her commitment to sharing information with state, local and tribal law enforcement and security to ensure those charged with protecting America’s communities against violence have access to the information they need about evolving threats of terrorism and violent extremism.

Still, not all recommendations for increased security at government buildings have been implemented 15 years after the bombing.