>>Only if they know that it is not a terrorist attack. They clearly don't know yet.
They've denied a number of attacks in the past until later information came out (information known and suppressed when the initial claim is made).
The DC Sniper Duo and the Tampa Teen Kamikaze Pilot are 2 such cases.
They will lie about such details even when they possess notes from the terrorists. Charles Bishop/Bishra's letter (on The Smoking Gun) included the phrase "terrorist acts" with the word terrorist crossed out but still legible. He or someone else crossed it out of his suicide note. If he really didn't feel he was engaging in "terrorism" he could've started over and left out the references praising Bin Laden and threatening a bomb at the Superbowl.
http://www.thesmokinggun.com/archive/tampasu1.html
Didn't Moose also downplay such notions when the DC police held Islamic terrorist rants from the Duo?