CHANDIGARH: The grenade blast in Chandigarh that occurred on Wednesday evening at the residence of a 100-year-old retired principal from Himachal Pradesh has been resolved by the Punjab Police in a joint operation with central agencies. The attack was masterminded by ISI-backed Pakistan-based terrorist Harwinder Singh, alias Rinda of Babbar Khalsa International, and USA-based Harpreet Singh, alias Happy Passia, with …