The key to success in this phase of preparation is to ensure the different law enforcement and intelligence agencies are sharing and exchanging information, thus providing the analysts with the data they need integrated with the accuracy they require.

Another critical pre-event task is ensuring that the personnel with the greatest access to the event -- staff, contractors and volunteers -- are trustworthy. Performing background checks is standard procedure. And, while background checks can be highly effective, for an event that is orders of magnitude greater than most other events, performing background checks can bump up against several challenges.

First is the classic "entity resolution" challenge. Information about any individual is likely going to be scattered across a range of databases. While one database may contain a red-flag item -- a pending drug charge or a secondary connection to a known terrorist -- another database may not. The challenge is bringing this information together to create a single record -- a "single version of the truth" -- about an individual or entity.

The second challenge is time. Performing background checks on thousands of individuals in a very short period of time can be daunting -- so much so, that the people involved in the process may look for shortcuts.