[fella]

Three suspects come to mind, ISIS, Turkey and Iran.

[spetznaz]

Only one suspect really - radical Sunni Islam. Virtually every single terrorist attack anywhere in the globe can be attributed to Sunni Islam. Be it in Iraq, Syria, Nigeria (Boko Haram), the US (911), Pakistan, India, Somalia and Kenya (Al Shabaab), the Philippines and Indonesia (Abu Sayyaf), you name it.

Overwhelmingly Sunni Islam, and supported by Saudi Arabia, Qatar and Pakistan.

Shia Islam (and Iran) have largely been involved in the last 15 years in places like the old Sadr city insurgency, and obviously groups like Hezbollah are Shia Islam/Iran supported. But all of those, combined, do not come close to Sunni based attacks around the world.

Virtually every other group, from ISIS to Al Qaeda to Al Nusra, are all Sunni based Islam. The Pakistani attack is 100% guaranteed a Sunni based terror group attack. Pakistani supported several such groups, since those groups would attack India, but lately they have been biting the hand that feeds them.