Killing Osama bin Laden was justified — he represented a threat to the Navy SEALs conducting their military operation and was stopped — close that chapter. However, al-Qaida and other terrorist organizations will continue planning attacks against U.S. targets, and we need to increase our vigilance.

 The operation proved that our intelligence community and our military can effectively coordinate and execute a high-risk, sensitive mission of global importance and strategic significance.

But this did not happen overnight.

In the years since 9/11, the integration of previously stovepiped government intelligence agencies worked to increase cooperation and information-sharing that has benefited our government tremendously.

All public signs point to a significant intelligence accumulation from the compound in Abbottabad, Pakistan, where bin Laden had lived for more than five years. National Security Adviser Tom Donilon called the cache “the size of a small college library,” distinguishing it as among the most significant intelligence acquisitions in U.S. history.

Establishing a secure American homeland has always required both offense and defense. Never was that more clear than in the days after 9/11, when the Office of Homeland Security and its successor, the Department of Homeland Security, were organized and created, while we were attacking al-Qaida in Afghanistan to remove its sanctuary.

Our counterterrorism efforts these past weeks mark significant accomplishments for our intelligence and special operations offensive efforts. Without a doubt, the al-Qaida leadership will be on the run at least for the short term. But regrettably that won’t stop lower-level and independent operators from taking their inspiration from bin Laden’s death to plot their revenge.

We need to stay on guard.

As the 10-year anniversary of 9/11 approaches, our baseline level of homeland defense has significantly increased, and not just in the aviation sector. The United States has taken major steps forward in assessing and hardening our critical infrastructure, training state and local law enforcement, screening cargo security and strengthening our borders. Perhaps the most important element is an engaged public, which continues to remain vigilant as the harsh memory of 9/11 fades.

Two recent nearly successful terrorist attacks in the U.S. provide a window into what al-Qaida and its loose network of supporters and operatives aspire to do, and how we should respond.

On May 1, 2010, a Pakistani vice admiral’s 31-year-old son, Faisal Shahzad, who had recently become a U.S. citizen and was living in Connecticut, attempted to set off a homemade car bomb in Manhattan’s Times Square. He was arrested two days later boarding a flight at JFK airport bound for Dubai, attempting to return to his family in Pakistan. Shahzad recently pleaded guilty and received a life sentence. The key factor that neutralized the threat was two street vendors who alerted local police to a parked car with a smoking engine. The bomb had ignited but not detonated, and it was successfully disarmed.

Imagine the absolute panic that would have occurred if a car bomb detonated in Manhattan? Thankfully it did not, but it might have were it not for two alert citizens. This is the type of vigilance that will be required by Americans as we move forward into an era of potential post-bin Laden retaliatory attacks.

The second important recent attempt was the “underwear bomber,” who attempted to blow up a Detroit-bound international airliner on Christmas Day 2009. That attempted terrorist, Umar Farouk Abdulmutallab, was a Nigerian who had received training in Yemen, had al-Qaida ties and who never should have been allowed on a commercial jet. His own father told the U.S. Embassy in Lagos that his son was becoming radicalized. Fortunately, the explosives only created a small fire, which was extinguished; unfortunately, the explosives that he brought onboard went undetected.

Again, imagine the economic, psychological and political effect of a commercial airliner blowing up in the air over America on Christmas Day. In this case, American intelligence failed to flag Abdulmutallab, and aviation security procedures did not detect the combination of PETN and TATP, the same combination used by attempted airline bomber Richard Reid in 2001.

We have reduced our nation’s vulnerabilities, but we need to continue the momentum.

American security forces are still using technology that was developed and deployed immediately after the 9/11 attacks to protect against a terrorist capability that has clearly evolved over time. In the post-bin Laden world of al-Qaida, we are likely to see further splintering of international terrorists and the creation of new, loosely connected terrorist networks that may act independently but share broader goals. Put simply, bring fewer large-scale, coordinated attacks such as 9/11 and more attempted attacks such as the underwear bomber and the Times Square bomber.

We need to get better technology in the field to counter the threats before the terrorists mount their next attack, not in response to their attacks. We need to continue our offensive intelligence, military and law enforcement efforts, as well as continue increasing our defensive efforts on our mass-transit systems and soft targets.

Our successes increase the urgency of our future efforts. As former CIA Director Michael Hayden said, in war, you should “reinforce success.” We have succeeded in our recent offensive efforts, but we also need more success on defense.

Robert Liscouski served as assistant secretary for infrastructure protection at the Department of Homeland Security from 2003 to 2005 and now heads Secure Strategy Group.