But around the nation, politicians and security experts were questioning Ms Napolitano’s assessment, particularly in light of Umar Farouk Abdulmutallab’s father, a former Nigerian government minister, notifying the US embassy in Abuja six months ago of his son’s increasingly radical views and that he had travelled to Yemen.

Umaru Abdulmutallab expressed surprise over the weekend that his son had been permitted to fly.

The younger Abdulmutallab had been put on a broad watchlist, the Terrorist Identities Datamart Environment, which contains more than 500,000 names and is shared by law enforcement agencies.

But his visa to enter the US was not revoked and he was not put on the no-fly list or the list that would have required additional screening.

The real reason the terrorism watchlist wasn’t taken seriously:

Dear Department of Homeland Security,

I am a former Nigerian government minister and I am writing to you with very important information.  My son …

Mark as spam.