I heard that there were many abnormalities with the visas held by the terrorists. No specifics, where they expired?
They were retarded kines of abnormalities, like extremely bad grammar, barely legible, fake city names, claiming to be married but not filling in information about a spouse, huge areas of the applications missing, etc. There is no reason they should have ever been accepted.
And yes, several of them had overstayed their Visas, and were thus illegally in the country.