Can anybody answer why the Delhi blast took place??

Today, around 6.00 pm serial blasts rocked Delhi. It is a day before the ganeshotsav festival concludes. Security has been tightened in Mumbai but it is a frequent news now. The terrorist sent a mail 5 minutes before the blast. Uncensored images were flashed on TV channels minutes after the blast. Its time that these terrorists should understand that their gimmick to spread terror is worthless. What are they getting out of the act?? Some moments to cherish on various TV channels with dead people on the streets. If these terrorists are the citizen of our country, they should realise that they are hurting, terrorising their own people.