All we can do is speculate -
This is no speculation this is clear army has spooks inside who are sold cheap and giving away targets ! how does these attackers get in GHQ than this mosque , its obvious they knew & have the full intel about security inside both premises! Bigger question is who are these rats and why are they doing this? and how could PA crush em?
Also Boss if they are getting helped by foreignors than they are more dangerous than TTP ,Raw ,Mosad or may b the Mars Intl agency
I don't understand why people keep repeating that they got inside the GHQ, while in reality they did not. All they could do was get to the security compound where visitors would used to come and passes either got issued for entering GHQ or the person for whom the visitor had come, would come to this compound and meet the guest. So reaching this place was no big issue as there was only one check post before you reach this compound where the 2nd check post was and then further on other security arrangements in place and the major factor that lead them inside to this compound was their uniform which confused the guys at the security compound thinking them their own otherwise they would have been taken down too just like other 4. Plus, the captured militant Dr.Usman is ex-army having been worked in AMC corps and was ex-assistant to Lt Gen Mushtaq whom he later assassinated. Ex-soldiers having joined these takfiri ranks is no hidden fact, even some brainwashed ex-officers joining them is not hidden fact too. So with ex-service guys in their ranks, having such information is no big problem, even i being a civilian and hundreds of others like me know well who goes to which Masjid and where those Masjids are. And guessing about security arrangements is no big problem too, as we see those arrangement on daily basis and finding loop holes is no big issue and these guys don't plan such attacks in a day or two, weeks, months take for such preparations and they already have planned targets on which preparations has already been done, just final touches are given when order to execute them is given.
Do remember, in the assassination attempt on Musharaf, ex-SSG guy had helped these takfiri thugs just for money.
It was a normal masjid in a military residential area, where civilians could come too and for these thugs knowing the security layout was no big deal.