First of all, the attackers went right to the local police station and attacked it. Clearly meant to reduce command and control of the counter. Whether by luck or by design, they were able to take out the top three terror cops at that station.

According to some sources, while there are many anti-terror groups within the security forces, they are not typically tasked together with any type of linear, interactive or interchangable leadership. Basically, city, province, state then military. Obviously, the city police are meant to be the first responders. With the local police assaulted and thrown off stride, their response time and efforts would be definitely thrown off and coordination with other units or up the line would be hindered. With the top cop and his two deputies gone, there would be a question of who takes over command as well, well before any other response teams could arrive and then as they appeared.

One has only to look at local law enforcement politics to understand that there would be a lot of people running around thinking they were now in charge and should issue orders. a bunch of which would be contradictory and possibly non-sensical. So, while the headquarters is in chaos and the LEO on the beat are out with limited instruction or communication, the terrorists get a nice little window of time to go about their business with little interdiction.

This is one factor that has me very sure that this was not a local group nor a "new group" accept to say a group claiming some other name as their "corps" name. LeT, probably, but I bet there is some higher org and experience that provided the training, facilitation and strategic planning.