Bomb blast at the gate of delhi hc-who is responsible?

Today around a powerful blast took place at 10:15 am this morning at  the Delhi High Court at Gate no 5. Police said 10 people have died and about 56 people have been been injured; six of them have been described as being in very critical condition.

After 1:30 our HM P Chidambaram today said intelligence about threats were shared with Delhi Police in July.

The question lies who is responsilbe???? What is the benefit in calling high alert which should have been raised much before August even..